LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


SOI  L.  S 


AND 


FERTILIZERS 


BY 


HARRY  SNYDER,  B.S. 

PROFESSOR  OF  AGRICULTURAL  CHEMISTRY,  UNIVERSITY  OF 

MINNESOTA,  AND  CHEMIST  OF  THE  MINNESOTA 

EXPERIMENT   STATION 


SECOOND    EC  DJ  T  I  O  N 
^v.TTXHv^ 

^     O-  THE  X 

UNIVERSITY   1 


OF 


EASTON,  PA.: 
THE  CHEMICAL  PUBLISHING  CO. 

1905. 
(ALL  RIGHTS  RESERVED) 


COPYRIGHT,  1899,  BY  EDWARD  HART. 

1905,    " 


PREFACE  TO  SECOND  EDITION 

The  first  edition  of -this  work  was  published  under 
the  title  "  The  Chemistry  of  Soils  and  Fertilizers."  In 
the  revision  of  the  text  the  subject  matter  has  been 
entirely  rewritten,  new  material  has  been  added,  and 
the  laboratory  practice  has  been  made  a  more  promi- 
nent feature.  These  additions  have  changed  the  scope 
of  the  book  to  such  an  extent  as  to  necessitate  a  change 
of  name.  The  work  as  now  presented  includes  all  of 
the  topics  and  laboratory  practice  relating  to  soils  as 
outlined  by  the  Committee  on  methods  of  teaching 
Agriculture,  appointed  by  the  Association  of  Agricul- 
tural Colleges  and  Experiment  Stations.  The  aim  of 
the  book  as  presented  in  the  preface  ro  the  first  edition 
has  been  kept  in  view  in  the  preparation  of  the  second 
edition. 

HARRY  SNYDER. 
UNIVERSITY  OF  MINNESOTA, 

COLLEGE  OF  AGRICULTURE, 
ST.  ANTHONY  PARK,  MINN. 

June  i ,  1905. 


PREFACE   TO  FIRST  EDITION. 


For  several  years  courses  of  instruction  have  been 
given  at  the  University  of  Minnesota  to  classes  of 
young  men  who  intend  to  become  farmers  and  who 
desire  information  that  will  be  of  assistance  to  them 
in  their  profession.  In  giving  this  instruction  mimeo- 
graphed notes  have  been  prepared,  but  the  increase 
in  the  number  of  students  and  the  volume  of  notes 
necessitate  the  publication  of  this  work.  In  its  prep- 
aration, it  has  been  the  aim  to  give,  in  condensed 
form,  the  principles  of  chemistry  which  have  a  bear- 
ing upon  the  conservation  of  soil  fertility  and  the 
economic  use  of  manures. 

HARRY  SNYDER. 
UNIVERSITY  OF  MINNESOTA, 
COLLEGE  OF  AGRICULTURE, 

ST.  ANTHONY  PARK,  MINN. 
April  75,  1899. 


CONTENTS 


INTRODUCTION 

Early  uses  of  manures  and  explanation  of  their  action  by  alche- 
mists;  Investigations  prior  to  1800  :  Work  of  De  Saussure,  Davy, 
Thaer,  and  Boussingault ;  Liebig's  writings  and  their  influence ; 
Investigations  of  Lawes  and  Gilbert ;  Contributions  of  other  in- 
vestigators ;  Agronomy  ;  Value  of  soil  studies.  Pages  i-S. 

CHAPTER  I 

Physical  Properties  of  Soils. — Chemical  and  physical  properties 
of  soils  considered  ;  Weight  of  soils  ;  Size  of  soil  particles  ;  Clay ; 
Sand  ;  Silt ;  Form  of  soil  particles  ;  Number  and  arrangement  of 
soil  particles  ;  Mechanical  analysis  of  soils  ;  Crop  growth  and  phys- 
ical properties.  Soil  types — Potato  and  truck  soils ;  Fruit  soils  ; 
Corn  soils  ;  Medium  grass  and  grain  soils  ;  Wheat  soils ;  Sandy, 
clay  and  loam  soils.  Relation  of  the  soil  to  water ;  Amount  of 
water  required  for  crops  ;  Bottom  water  ;  Capillary  water  ;  Hydro- 
scopic  water  ;  Loss  of  water  by  percolation,  evaporation  and  trans- 
piration ;  Drainage  influence  of  forest  regions  ;  Influence  of  culti- 
vation upon  the  water  supply  of  crops  ;  Capillary  water  and  culti- 
vation ;  Shallow  surface  cultivation  ;  Cultivation  after  rains  ;  Roll- 
ing ;  Sub-soiling  ;  Fall  plowing;  Spring  plowing ;  Mulching;  Depth 
of  plowing  ;  Permeability  of  soils  ;  Fertilizers  and  their  Influence 
upon  moisture  content  of  soils  ;  Farm  manures  and  soil  moisture  ; 
Relation  of  soils  to  heat  ;  Heat  from  chemical  reactions  within  the 
soil ;  Heat  and  crop  growth  ;  Organic  matter  and  iron  compounds  ; 
Color  of  soils  ;  Odor  and  taste  of  soils  ;  Power  to  absorb  gases  ; 
Relation  of  soils  to  electricity  ;  Importance  of  physical  properties 
of  the  soil.  Pages  9-44. 

CHAPTER  II 

Geological  Formation  and  Classification  of  Soils.  —  Agricultural 
geology  ;  Formation  of  soils  ;  Action  of  heat  and  cold  ;  Action  of 
water  ;  Glacial  action  ;  Chemical  action  of  water  ;  Action  of  air  and 
gases  ;  Action  of  micro-organism  ;  Action  of  vegetation  ;  Combined 
action  of  the  various  agents  ;  Distribution  of  soils  ;  Sedentary  and 


VI  CONTENTS 

transported  soils  ;  Rocks  and  minerals  from  which  soils  are  derived 
as  quartz,  feldspar,  mica,  hornblende,  zeolites,  granite,  apatite, 
kaolin  ;  Disintegration  of  rocks  and  minerals  ;  Value  of  geological 
study  of  soils.  Pages  45-56. 

CHAPTER  III 

Chemical  Composition  of  Soils. — Elements  present  in  soils  ;  Clas- 
sification of  elements  ;  Combination  of  elements  ;  Forms  in  which 
elements  are  present  in  soils ;  Acid-forming  elements,  silicon, 
double  silicates,  carbon,  sulphur,  chlorine,  phosphorus,  nitrogen, 
oxygen,  hydrogen;  Base-forming  elements,  aluminum,  potassium, 
calcium,  magnesium,  sodium,  iron  ;  Forms  of  plant  food  ;  Amount 
of  plant  food  in  different  forms  in  various  types  of  soils  ;  How  a 
soil  analysis  is  made  ;  Value  of  soil  analysis  ;  Interpretation  of  the 
results  of  soil  analysis  ;  Use  of  dilute  acids  as  solvents  in  soil  anal- 
ysis ;  Distribution  of  plant  food  in  the  soil ;  Composition  of  typical 
soils ;  "Alkali  "  soils  and  their  improvement ;  Acid  soils  ;  Organic 
compounds  of  soil ;  Sources;  Classification;  Humus;  Hutuates  ; 
Humification  ;  Humates  produced  by  different  kinds  of  organic 
matter;  Value  of  humates  as  plant  food,  amount  of  plant  food  in 
humic  forms  ;  Physical  properties  of  soils  influenced  by  humus  ; 
Loss  of  humus  by  forest  fires,  by  prairie  fires,  by  cultivation  ; 
Humic  acid  ;  Soils  in  need  of  humus ;  Soils  not  in  need  of  humus  ; 
Composition  of  humus  from  old  and  new  soils  ;  Influence  of  differ- 
ent methods  of  farming  upon  humus.  Pages  57-96. 

CHAPTER  IV 

Nitrogen  of  the  Soil  and  Air,  Nitrification  and  Nitrogenous 
Manures. — Importance  of  nitrogen  as  plant  food  ;  Atmospheric 
nitrogen  as  a  source  of  plant  food.  Experiments  of  Boussingault, 
Ville,  and  Lawes  and  Gilbert;  Result  of  field  trials  ;  Experiments 
of  Hellriegel  and  Wilfarth  and  recent  investigators  ;  Composition 
of  root  nodules  ;  Amount  of  nitrogen  returned  to  soil  by  legumi- 
nous crops  and  importance  to  agriculture  ;  Nitrogenous  compounds 
of  the  soil ;  Origin  ;  Organic  nitrogen  ;  Amount  of  nitrogen  in 
soils  ;  Removed  in  crops  ;  Nitrates  and  nitrites  ;  Ammonium  com- 
pounds ;  Ammonia  in  rain  and  drain  waters  ;  Ratio  of  nitrogen  to 
carbon  in  the  soil  ;  Losses  of  nitrogen  from  soils  ;  Gains  of  nitrogen 
to  soils;  Nitrification;  Former  views  regarding  ;  Workings  of  an 
organism  ;  Conditions  necessary  for  nitrification  ;  Influence  of  cul- 


CONTENTS  Vll 

tivation  upon  these  conditions  ;  Nitrous  acid  organisms,  ammonia- 
producing  organisms,  denitrification,  number  and  kind  of  organ- 
isms in  soils  ;  Inoculation  of  soils  with  organisms  ;  Chemical  pro- 
ducts produced  by  organisms  ;  Losses  of  nitrogen  by  fallowing  rich 
prairie  lands;  Influence  of  plowing  upon  nitrification  ;  Nitrogenous 
manures  ;  Sources  ;  Dried  blood,  tankage,  flesh  meal,  fish  scrap, 
seed  residue,  and  uses  of  each  ;  Leather,  wool  waste  and  hair ; 
Peat  and  muck  ;  Leguminous  crops  as  nitrogenous  fertilizers  ;  Sod- 
ium nitrate,  ammonium  salts  ;  Cost  and  value  of  nitrogenous  fer- 
tilizers. Pages  97-130. 

CHAPTER  V 

Farm  Manures. — Variable  composition  of  farm  manures  ;  Average 
composition  of  manures  ;  Factors  which  influence  composition  of 
manures  ;  Absorbents  ;  Use  of  peat  and  muck  as  absorbents  ;  Rela- 
tion of  food  consumed  to  manures  produced  ;  Bulky  and  concen- 
trated foods  ;  Course  of  the  nitrogen  of  the  food  during  digestion  ; 
Composition  of  liquid  and  solid  excrements;  Manurial  value  of 
foods;  Commercial  valuation  of  manure;  Influence  of  age  and 
kind  of  animal;  Manure  from  young  and  old  animals ;  Cow  ma- 
nure ;  Horse  manure  ;  Sheep  manure  ;  Hog  manure  ;  Hen  manure; 
Mixing  manures  ;  Volatile  products  from  manure  ;  Human  excre- 
ments ;  Preservation  of  manures  ;  Leaching  ;  Losses  by  fermenta- 
tion ;  Different  kinds  of  fermentation  ;  Water  necessary  for  fermen- 
tation ;  Heat  produced  during  fermentation  ;  Composting  manures; 
Uses  of  preservatives  ;  Manure  produced  in  sheds;  Value  of  pro- 
tected manure ;  Use  of  manures  ;  Direct  hauling  to  field  ;  Coarse 
manures  may  be  injurious  ;  Manuring  pasture  land  ;  Small  piles  of 
manure  in  fields  objectionable  ;  Rate  of  application  ;  Most  suitable 
crops  to  apply  to  ;  Comparative  value  of  manure  and  food  ;  Lasting 
effects  of  manure  ;  Comparative  value  of  good  and  poor  manure  ; 
Summary  of  ways  in  which  manures  may  be  beneficial.  Pages 

I3I-I59. 

CHAPTER  VI 

Fixation. — Fixation  a  chemical  change,  examples  of  ;  Due  to 
zeolites  ;  Humus  and  fixation  ;  Soils  possess  different  powers  of  fix- 
ation ;  Nitrates  do  not  undergo  fixation  ;  Fixation  of  ammonia ; 
Fixation  may  make  plant  food  less  available  ;  Fixation  a  desirable 
property  of  soils  ;  Fixation  and  the  action  of  manures.  Pages 
160-163. 


Vlll  CONTENTS 

CHAPTER  VII 

Phosphate  Fertilizers. — Importance  of  phosphorus  as  plant  food  ; 
Amount  removed  in  crops  ;  Amount  and  source  of  phosphoric  acid 
in  soils  ;  Commercial  forms  of  phosphoric  acid  ;  Phosphate  rock  ; 
Calcium  phosphates ;  Reverted  phosphoric  acid  ;  Available  phos- 
phoric acid;  Manufacture  of  phosphate  fertilizers,  acid  phosphates, 
superphosphates  ;  Commercial  value  of  phosphoric  acid  ;  Basic  slag 
phosphates ;  Guano ;  Bones  ;  Steamed  bone  ;  Dissolved  bone  ;  Bone 
black  ;  Use  of  phosphate  fertilizers ;  How  to  keep  the  phosphoric 
acid  of  the  soil  available.  Pages  164-176. 

CHAPTER  VIII 

Potash  Fertilizers. — Potassium  an  essential  element;  Amount  of 
potash  removed  in  crops  ;  Amount  in  soils  ;  Source  of  soil  potash  ; 
Commercial  forms  of  potash ;  Stassfurt  salts,  occurrence  of ; 
Kainit  ;  Muriate  of  potash  ;  Sulphate  of  potash ;  Other  Stassfurt 
salts  ;  Wood  ashes,  composition  of;  Amount  of  ash  in  different 
kinds  of  wood  ;  Action  of  ashes  on  soils;  Leached  ashes  ;  The  alka- 
linity of  ashes;  Coal  ashes;  Miscellaneous  ashes;  Commercial 
value  of  potash ;  Use  of  potash  fertilizers ;  Joint  use  of  potash 
and  lime.  Pages  177-186. 

CHAPTER  IX 

Lime  and  Miscellaneous  Fertilizers. — Calcium  an  essential  ele- 
ment ;  Amount  of  lime  removed  in  crops  ;  Amount  of  lime  in  soils  ; 
Different  kinds  of  lime  fertilizers;  Their  physical  and  chemical 
action  ;  Action  of  lime  upon  organic  matter  and  correcting  acidity 
of  soils  ;  Lime  liberates  potash  ;  Aids  nitrification  ;  Action  of  land 
plaster  on  some  "alkali  "  soils  ;  Quicklime  and  slaked  lime  ;  Pul- 
verized lime  rock  ;  Marl ;  Physical  action  of  lime  ;  Judicious  use  of 
lime ;  Miscellaneous  fertilizers ;  Salt  and  its  action  on  the  soil ; 
Magnesium  salts  ;  Soot ;  Sea-weed  ;  Strand  plant  ash  ;  Wool  wash- 
ings ;  Street  sweepings.  Pages  187-195. 

CHAPTER  X 

Commercial  Fertilizers. —History  of  development  of  industry; 
Complete  fertilizers  and  amendments  ;  Variable  composition  of 
commercial  fertilizers  ;  Preparation  of  fertilizers  ;  Inert  forms  of 
matter  in  fertilizers  ;  Inspection  of  fertilizers  ;  Mechanical  condi- 


CONTENTS  IX 

tion  of  fertilizers  ;  Forms  of  nitrogen,  phosphoric  acid  and  potash 
in  commercial  fertilizers;  Misleading  statements  on  fertilizer  bags  ; 
Estimating  the  value  of  a  fertilizer  ;  Home  mixing  ;  Fertilizers  and 
tillage  ;  Abuse  of  commercial  fertilizers  ;  Judicious  use  of  ;  Field 
tests  ;  Preliminary  experiments  ;  Verifying  results  ;  Deficiency  of 
nitrogen,  phosphoric  acid,  potash  and  of  two  elements  ;  Import- 
ance of  field  trials  ;  Will  it  pay  to  use  fertilizers?  Amount  to  use 
per  acre  ;  Influence  of  excessive  applications  ;  Fertilizing  special 
crops;  Commercial  fertilizers  and  farm  manures.  Pages  196-214. 

CHAPTER  XI 

Food  Requirements  of  Crops. — Amount  of  fertility  removed  by 
crops ;  Assimilative  powers  of  crops  compared  ;  Way  in  which 
plants  obtain  their  food  ;  Cereal  crops,  general  food  requirements  ; 
Wheat ;  Barley  ;  Oats;  Corn  ;  Miscellaneous  crops  ;  Flax  ;  Potatoes  ; 
Sugar-beets  ;  Roots  ;  Turnips  ;  Rape  ;  Buckwheat  ;  Cotton  ;  Hops  ; 
Hay  and  grass  crops  ;  Leguminous  crops  ;  Garden  crops  ;  Fruit 
trees  ;  Lawns.  Pages  217-229. 

CHAPTER  XII 

Rotation  of  Crops.— Object  of  rotating  crops;  Principles  involved 
in  crop  rotation  ;  Deep  and  shallow  rooted  crops  ;  Humus-consum- 
ing and  humus-producing  crops  ;  Crop  residues  ;  Nitrogen-consum- 
ing and  nitrogen-producing  crops  ;  Rotation  and  mechanical  con- 
dition of  soil  ;  Economic  use  of  soil  water ;  Rotation  and  farm 
labor  ;  Economic  use  of  manures  ;  Salable  crops  ;  Rotations  advan- 
tageous in  other  ways  ;  Long-  and  short-course  rotations  ;  Problems 
in  rotations  ;  Conservation  of  fertility  ;  Necessity  of  manures;  Use 
of  crops  ;  Two  systems  of  farming  compared  ;  Losses  of  fertility 
with  different  methods  of  farming  ;  Problems  on  income  and  outgo 
of  fertility  from  farm.  Pages  230-246. 

CHAPTER  XIII 

Preparation  of  Soils  for  Crops,  —  Importance  of  good  physical 
condition  of  seed  bed  ;  Influence  of  Methods  of  Plowing  upon 
the  condition  of  the  seed  bed  ;  Influence  of  moisture  content  of 
the  soil  at  the  time  of  plowing  ;  Influence  upon  the  seed 
bed  of  pulverizing  and  fining  the  soil  ;  Aeration  of  seed  bed 
necessary  ;  Preparation  of  seed  bed  without  plowing ;  Mixing 
of  sub  soil  with  seed  bed ;  Cultivation  to  destroy  weeds  ; 


X  CONTENTS 

Influence  of  cultivation  upon  bacterial  action  ;  Inoculation  of 
soils  ;  Cultivation  for  special  crops  ;  Cultivation  to  prevent  washing 
and  gullying  of  lands  ;  Bacterial  diseases  of  soils ;  Influence  of 
crowding  of  plants  in  the  seed  bed  ;  Selection  of  crops  ;  Inherent 
and  cumulative  fertility  of  soils  ;  Balanced  soil  conditions.  Pages 
247-260. 

CHAPTER  XIV 

Laboratory  Practice.— General  directions  ;  Notebook  ;  Apparatus 
used  in  work  ;  Determination  of  Hydroscopic  moisture  of  soils  ; 
Determination  of  the  capacity  of  loose  soils  to  absorb  water  ;  Deter- 
mination of  Capillary  water  of  soils  ;  Capillary  action  of  water  upon 
soils  ;  Influence  of  manure  and  shallow  surface  cultivation  upon 
moisture  content  and  temperature  of  soils  ;  Weight  of  soils  ;  Influ- 
ence of  color  upon  the  temperature  of  soils ;  Rate  of  movement  of  air 
through  soils  ;  Separation  of  sand,  silt  and  clay  ;  Sedimentation  of 
clay  ;  Properties  of  rocks  from  which  man}'  soils  are  derived  ;  Form 
and  size  of  soil  particles ;  Pulverized  rock  particles ;  Reaction  of 
soils  ;  Absorption  of  gases  by  soils  ;  Acid  insoluble  matter  of  soils  ; 
Acid  soluble  matter  of  soils  ;  Extraction  of  humus  from  soils  ;  Nit- 
rogen in  soils ;  Testing  for  nitrates  ;  Volatilization  of  ammonium 
salts  ;  Testing  for  phosphoric  acid  ;  Preparation  of  acid  phosphate  ; 
Solubility  of  organic  nitrogenous  compounds  in  pepsin  solution; 
Preparation  of  fertilizers  ;  Testing  ashes  ;  Extracting  water  soluble 
materials  from  a  commercial  fertilizer  ;  Influences  of  continuous 
cultivation  and  crop  rotation  upon  the  properties  of  soil  ;  Sum- 
mary of  results  with  tests  of  home  soil.  Pages  261-274. 

References  ;  Review  Questions.     Index,  pages  275-283,  284-287. 


OF  THE 

UNIVERSITY 

OF 


SOILS  AND  FERTILIZERS 


INTRODUCTION 

Prior  to  1800  but  little  was  known  of  the  sources 
and  importance  of  plant  food.  Manures  had  been 
used  from  the  earliest  times,  and  their  value  was  rec- 
ognized, although  the  fundamental  principles  under- 
lying their  use  were  not  understood.  It  was  believed 
that  they  acted  in  some  mysterious  way.  The  alche- 
mists had  advanced  various  views  regarding  their  ac- 
tion ;  one  was  that  the  so-called  "  spirits  "  left  the  de- 
caying manure  and  entered  the  plant,  producing  more 
vigorous  growth.  As  evidence,  the  worthless  charac- 
ter of  leached  manure  was  cited.  It  was  thought  that 
the  spirits  had  left  such  manure.  The  terms  (  spirits 
of  hartshorn',  'spirits  of  niter',  'spirits  of  turpentine ' 
and  many  others  reflect  these  ideas  regarding  the  com- 
position of  matter. 

The  alchemists  held  that  one  substance,  like  copper, 
could  be  changed  to  another  substance,  as  gold.  Plants 
were  supposed  to  be  water  transmuted  in  some  mys- 
terious way  directly  into  plant  tissue.  Van  Helmont, 
in  the  seventeenth  century,  attempted  to  prove  this. 
"  He  took  a  large  earthen  vessel  and  filled  it  with  200 
pounds  of  dried  earth.  In  it  he  planted  a  willow 
weighing  5  pounds,  which  he  duly  watered  with  rain 

(i) 


2  SOILS   AND    FERTILIZERS 

and  distilled  water.  After  five  years  he  pulled  up  the 
willow  and  it  now  weighed  169  pounds  and  3  ounces." * 
He  concluded  that  164  pounds  of  roots,  bark,  leaves, 
and  branches  had  been  produced  by  the  direct  trans- 
mutation of  the  water. 

It  is  evident  from  the  preceding  example  that  any- 
thing like  an  adequate  idea  of  the  growth  and  compo- 
sition of  plant  bodies  could  not  be  gained  until  the 
composition  of  air  and  water  was  established. 

The  discovery  of  oxygen  by  Priestly,  in  1774,  of 
the  composition  of  water  by  Cavendish  in  1781,  and 
of  the  role  which  carbon  dioxide  plays  in  plant  and 
animal  life  by  DeSaussure  and  others  in  1800,  form 
the  nucleus  of  our  present  knowledge  regarding  the 
sources  of  matter  stored  up  in  plants.  It  was  between 
1760  and  1800  that  alchemy  lost  its  grip,  because  of 
advances  in  knowledge,  and  the  way  was  opened  for 
the  development  of  modern  chemistry. 

The  work  of  DeSaussure,  entitled  "  Recherches  sur 
la  Vegetation,"  published  in  1804,  was  the  first  sys- 
tematic work  showing  the  sources  of  the  compounds 
stored  up  in  plant  bodies.  He  demonstrated,  quanti- 
tatively, that  the  increase  in  the  amount  of  carbon, 
hydrogen,  and  oxygen,  when  plants  were  exposed  to 
sunlight,  was  at  the  expense  of  the  carbon  dioxide  of 
the  air,  and  of  the  water  of  the  soil.  He  also  main- 
tained that  the  mineral  elements  derived  from  the  soil 
were  essential  for  plant  growth,  and  gave  the  results 
of  the  analyses  of  many  plant  ashes.  He  believed  that 
the  nitrogen  of  the  soil  was  the  main  source  of  the 
nitrogen  found  in  plants.  These  views  have  since 


INTRODUCTION  3 

been  verified  by  many  investigators,  and  are  substan- 
tially those  held  at  the  present  time  regarding  the 
fundamental  principles  of  plant  growth.  They  were 
not,  however,  accepted  as  conclusive  at  the  time,  and 
it  was  not  until  nearly  half  a  century  later,  when 
Boussingault,  Liebig,  and  others  repeated  the  investi- 
gations of  DeSaussure,  that  they  were  finally  accepted 
by  chemists  and  botanists. 

From  the  time  of  DeSaussure  to  1835,  scientific 
experiments  relating  to  plant  growth  were  not  actively 
prosecuted,  but  the  scientific  facts  which  had  accumu- 
lated were  studied,  and  attempts  were  made  to  apply 
the  results  to  actual  practice.  Among  the  first  to  see 
the  relation  between  chemistry  and  agriculture  was 
Sir  Humphry  Davy.  In  1813  he  published  his  "  Es- 
sentials of  Agricultural  Chemistry,"  which  treated  of 
the  composition  of  air,  soil,  manures,  and  plants,  and 
of  the  influence  of  light  and  heat  upon  plant  growth. 
About  this  same  period,  Thaer  published  an  important 
work  entitled  "  Principes  Raisonnes  d'  Agriculture." 
Thaer  believed  that  humus  determined  the  fertility  of 
the  soil,  that  plants  obtained  their  food  mainly  from 
humus,  and  that  the  carbon  compounds  of  plants  were 
produced  from  the  organic  carbon  compounds  of  the 
soil.  This  gave  rise  to  the  so-called  humus  theory, 
which  was  later  shown  to  be  an  inadequate  idea  re- 
garding the  source  of  plant  food,  and  for  a  time  it 
prevented  the  actual  value  of  humus  as  a  factor  of  soil 
fertility  from  being  recognized.  The  writings  of  Thaer 
were  of  a  most  practical  nature,  and  they  did  much  to 
stimulate  later  investigations. 


4  SOILS   AND   FERTILIZERS 

About  1830  there  was  renewed  interest  in  scientific 
investigations  relating  to  agriculture.  At  this  time 
Boussingault,  a  French  investigator,  became  actively 
engaged  in  agricultural  research.  He  was  the  first  to 
establish  a  chemical  laboratory  upon  a  farm,  and  to 
make  practical  investigations  in  connection  with  agri- 
culture. This  marks  the  establishment  of  the  first 
agricultural  experiment  station.  Boussingault's  work 
upon  the  assimilation  of  the  free  nitrogen  of  the  air  is 
reviewed  in  Chapter  IV.  His  study  of  the  rotation  of 
crops  was  a  valuable  contribution  to  agricultural 
science.  He  discovered  many  important  facts  relating 
to  the  chemical  characteristics  of  foods,  and  was  the 
first  to  make  a  comparative  study  of  the  amount  of 
nitrogen  in  different  kinds  of  foods  and  to  determine 
the  value  of  foods  on  the  basis  of  the  nitrogen  con- 
tent. His  study  of  the  production  of  saltpeter  did 
much  to  prepare  the  way  for  later  work  on  nitrifica- 
tion. The  investigations  of  Boussingault  covered  a 
variety  of  subjects  relating  to  plant  growth.  He  re- 
peated and  verified  much  of  the  earlier  work  of 
DeSaussure,  and  also  secured  many  additional  facts 
relating  to  the  chemistry  of  crop  growth.  As  to  the 
source  of  nitrogen  in  crops,  he  states  that :  "  The  soil 
furnishes  the  crops  with  mineral  alkaline  substances, 
provides  them  with  nitrogen,  by  ammonia  and  by 
nitrates,  which  are  formed  in  the  soil  at  the  expense 
of  the  nitrogenous  matters  contained  in  diluvium, 
which  is  the  basis  of  vegetable  earth  ;  compounds  in 
which  nitrogen  exists  in  stable  combination,  only  be- 
coming fertilizing  by  the  effect  of  time."  As  to  the 


INTRODUCTION  5 

absorption  of  the  gaseous  nitrogen  of  the  air  by  vege- 
table earth,  he  says :  "  I  am  not  acquainted  with  a 
single  irreproachable  observation  that  establishes  it ; 
not  only  does  the  earth  not  absorb  gaseous  nitrogen, 
but  it  gives  it  off."  2 

The  investigations  of  DeSaussure  and  Boussingault, 
and  the  writings  of  Davy,  Thaer,  Sprengel,  and  Schub- 
ler  prepared  the  way  for  the  work  and  writings  of 
Liebig.  In  1840  he  published  "Organic  Chemistry 
in  its  Applications  to  Agriculture  and  Physiology." 
Liebig's  agricultural  investigations  were  preceded  by 
many  valuable  discoveries  in  organic  chemistry,  which 
he  applied  directly  in  his  interpretations  of  agricul- 
tural problems.  His  writings  were  of  a  forcible  char- 
acter and  were  extremely  argumentative.  They  pro- 
voked, as  he  intended,  vigorous  discussions  upon 
agricultural  problems.  He  assailed  the  humus  theory 
of  Thaer,  and  held  that  humus  was  not  an  adequate 
source  of  the  plant's  carbon.  In  the  first  edition  of 
his  work  he  showed  that  farms  from  which  certain 
products  were  sold  naturally  became  less  productive, 
because  of  the  loss  of  nitrogen.  In  a  second  edition 
he  considered  that  the  combined  nitrogen  of  the  air 
was  sufficient  for  crop  production.  He  overestimated 
the  amount  of  ammonia  in  the  air,  and  underestimated 
the  value  of  the  nitrogen  in  soils  and  manures.  A 
study  of  the  composition  of  plant-ash  led  him  to 
propose  the  mineral  theory  of  plant  nutrition.  De- 
Saussure had  shown  that  plants  contained  certain 
mineral  elements,  but  he  did  not  emphasize  their  im- 
portance as  plant  food.  Liebig's  writings  on  the  com- 


6  SOILS   AND   FERTILIZERS 

position  of  plant-ash,  and  his  emphasizing  the  import- 
ance of  supplying  crops  with  mineral  food,  led  to  the 
commercial  preparation  of  manures,  which  in  later 
years  has  developed  into  the  commercial  fertilizer  in- 
dustry. The  work  of  L,iebig  was  not  conducted  in 
connection  with  field  experiments.  It  had,  however,  a 
most  stimulating  influence  upon  investigations  in  agri- 
cultural chemistry,  and  to  him  we  owe,  in  a  great  de- 
gree, the  summarizing  of  previous  disconnected  work 
and  the  mapping  out  of  valuable  lines  for  future  in- 
vestigations. 

Iviebig's  enthusiasm  for  agricultural  investigations 
may  be  judged  from  the  following  extract :  "I  shall 
be  happy  if  I  succeed  in  attracting  the  attention  of  men 
of  science  to  subjects  which  so  well  merit  to  engage 
their  talents  and  energies.  Perfect  agriculture  is  the 
true  foundation  of  trade  and  industry  ;  it  is  the  founda- 
tion of  the  riches  of  states.  But  a  rational  system 
of  agriculture  cannot  be  formed  without  the  applica- 
tion of  scientific  principles,  for  such  a  system  must  be 
based  on  an  exact  acquaintance  with  the  means  of 
nutrition  of  vegetables,  and  with  the  influence  of  soils, 
and  actions  of  manures  upon  them.  This  knowledge 
we  must  seek  from  chemistry,  which  teaches  the  mode 
of  investigating  the  composition  and  of  the  study  of 
the  character  of  the  different  substances  from  which 
plants  derive  their  nourishment."  3 

Soon  after  Liebig's  first  work  appeared,  the  investi- 
gations at  Rothamsted  by  Sir  J.  B.  Lawes  were  under- 
taken. The  most  extensive  systematic  work  in  both 
field  experiments  and  laboratory  investigations  ever 
conducted  have  been  carried  on  by  Lawes  and  Gilbert 


INTRODUCTION  7 

at  Rothamsted,  Eng.  Dr.  Gilbert  had  previously  been 
a  pupil  at  L,iebig,  and  his  becoming  associated  with 
Sir  J.  B.  La wes  marks  the  establishment  of  the  second 
experiment  station.  Many  of  the  Rothamsted  experi- 
ments have  been  continued  since  1844,  and  results  of 
the  greatest  value  io  agriculture  have  been  obtained. 
The  investigations  on  the  non-assimilation  of  the  at- 
mospheric nitrogen  by  crops,  published  in  1861,  were 
accepted  as  conclusive  evidence  upon  this  much-vexed 
question.  The  work  on  manures,  nitrification,  the 
nitrogen  supply  of  crops,  and  on  the  increase  and  de- 
crease of  the  nitrogen  of  the  soil  when  different  crops 
are  produced,  has  had  a  most  important  bearing  upon 
maintaining  the  fertility  of  soils. 

u  The  general  plan  of  the  field  experiments  has  been 
to  grow  some  of  the  most  important  crops  of  rotation, 
each  separately,  for  many  years  in  succession  on  the 
same  land,  without  manure,  with  farmyard  manure, 
and  with  a  great  variety  of  chemical  manures,  the 
same  kind  of  manure  being,  as  a  rule,  applied  year  after 
year  on  the  same  plot.  Experiments  with  different 
manures  on  the  mixed  herbage  of  permanent  grass 
land,  on  the  effects  of  fallow,  and  on  the  actual  course 
of  rotation  without  manure,  and  with  different  manures 
have  likewise  been  made."4 

In  addition  to  Davy,  Thaer,  DeSaussure,  Bous- 
singault,  Liebig,  and  Lawes  and  Gilbert,  a  great 
many  others  have  contributed  to  our  knowledge  of 
the  properties  of  soils.  The  work  of  Pasteur,  while 
it  did  not  directly  relate  to  soils,  indirectly  had  great 
influence  upon  soil  investigations.  His  researches 
upon  fermentation  made  it  possible  for  Schlosing  to 


8  SOILS   AND   FERTILIZERS 

prove  that  nitrification  was  the  result  of  the  workings 
of  living  organisms.  These  have  since  been  isolated 
and  studied  by  Warington  and  Winogradsky. 

During  recent  years  the  agricultural  experiment 
stations  of  this  and  other  countries  have  made  soils  a 
prominent  feature  of  their  work ;  some  of  the  results 
obtained  are  noted  in  the  following  chapters.  Our 
knowledge  regarding  the  chemistry,  physics,  geology 
and  bacteriology  of  soils  is  still  far  from  complete, 
bat  many  facts  have  been  discovered  which  are  of  the 
greatest  value  to  the  practical  farmer.  The  literature 
relating  to  soils  and  fertilizers  has  become  very  exten- 
sive, and  in  the  classification  of  agricultural  subjects 
for  study,  soil  forms  one  of  the  main  divisions  of 
agronomy. 

In  soil  investigations  it  has  frequently  happened, 
owing  to  imperfect  interpretation  of  results  and  to 
the  presence  of  many  modifying  influences,  that  the 
conclusions  of  one  investigator  appear  to  be  directly 
contradictory  to  those  of  another.  This  is  well 
illustrated  in  the  investigations  relating  to  the 
assimilation  of  free  atmospheric  nitrogen,  where 
seemingly  opposite  conclusions  now  form  a  complete 
theory. 

A  scientific  study  of  soils  is  valuable  from  an  edu- 
cational point  of  view,  as  well  as  because  the  practical 
knowledge  obtained  can  be  utilized  in  the  production 
of  crops.  In  the  cultivation  of  the  soil  it  should  be  the 
aim  to  conserve  the  fertility  and  to  produce  as  large 
yields  as  possible  of  the  most  valuable  crops.  This 
can  be  accomplished  only  as  the  result  of  a  thorough 
knowledge  of  soils  and  fertilizers. 


CHAPTER  I 

PHYSICAL  PROPERTIES  OF  SOILS 

1.  Soil. — Soil  is  disintegrated  and  pulverized  rock 
mixed  with  animal  and  vegetable  matter.     The  rock 
particles  are  of  different  kinds  and  sizes,  and  are  in 
various  stages   of   decomposition.     If   two   soils   are 
formed  from  the  same  kind  of  rock  and  differ  only  in 
the  size  of  the  particles,  the  difference  is  merely  a 
physical  one.     If,  however,  one  soil  is  formed  largely 
from  sandstone,  while  the  other  is  formed  from  lime- 
stone, the  difference  is  both  physical  and   chemical. 
Hence  it  is  that  soils  differ  both  physically  and  chem- 
ically.    It  is  difficult  to  consider  the  physical  proper- 
ties of  a  soil   without  also  considering  the  chemical 
properties.     The   chemical   and    physical    properties, 
when  jointly  considered,  determine  largely  the  agri- 
cultural value  of  a  soil. 

2.  Physical    Properties    Defined.  —  The   physical 
properties  of  a  soil  are  : 

1.  Weight. 

2.  Color. 

3.  Size,  form,  and  arrangement  of  the  soil  particles. 

4.  The  relation  of  the  soil  to  water,  heat,  and  cold. 

5.  Odor  and  taste. 

6.  The  relation  of  the  soil  to  electricity. 

3.  Weight. — Soils  differ  in  weight  according  to  the 
composition  and  size  of  the  particles.  Fine  sandy 
soils  weigh  heaviest,  while  peaty  soils  are  lightest  in 


10  SOILS   AND   FERTILIZERS 

weight.  But  when  saturated  with  water,  a  cubic  foot 
of  peaty  soil  weighs  more  than  a  cubic  foot  of  sandy 
soil.  Clay  soils  weigh  less  per  cubic  foot  than  sandy 
soils.  The  larger  the  amount  of  organic  matter  in  a 
soil  the  less  the  weight.  Pasture  land,  for  example, 
weighs  less  per  cubic  foot  than  arable  land.  Weight 
is  an  important  property  to  consider  when  the  total 
amounts  of  plant  food  in  two  soils  are  compared.  A 
peaty  soil  containing  i  per  cent,  of  nitrogen  and 
weighing  30  pounds  per  cubic  foot  has  less  total  nitro- 
gen than  a  soil  containing  0.40  per  cent,  of  nitrogen 
and  weighing  80  pounds  per  cubic  foot. 

The  weight  of  soils  per  cubic  foot  is  approximately 
as  follows : 5 

Pounds. 

Clay  soil 70  to    75 

Fine  sandy  soil 95  to  1 10 

Loam  soil 75  to    90 

Peaty  soil 25  to    60 

Average  prairie  soil 75 

Uncultivated  prairie  soil 65 

Figures  for  the  weight  per  cubic  foot  and  specific 
gravity  of  soils  are  on  the  basis  of  the  dry  soil.  When 
taken  from  the  field  the  weight  per  cubic  foot  varies 
with  the  amount  of  water  present. 

The  volume  of  a  soil  varies  with  the  conditions  to 
which  it  has  been  subjected.  Usually  about  50  per 
cent,  of  the  volume  is  air  space.  A  cubic  foot  of  soil 
from  a  field  which  has  been  well  cultivated  weighs 
less  than  from  a  field  where  the  soil  has  been  com- 
pacted. Hence  it  is  that  soils  have  both  a  real  and 
an  apparent  specific  gravity.  The  apparent  specific 


SIZE   OF   SOIL   PARTICLES  II 

gravity  of  a  soil  is  sometimes  less  than  half  of  the  real 
specific  gravity.  The  specific  gravity  of  different  soils 
as  given  by  Shoen  is  as  follows : 6 

Specific  gravity. 

Clay  soil • • 2.65 

Sandy  soil 2.67 

Fine  soil 2.71 

Humus  soil 2.53 

4,  Size  of  Soil  Particles.— The  size  of  soil  particles 
varies  from  those  hardly  distinguishable  with  the 
microscope  to  coarse  rock  fragments.  The  size  of  the 
particles  determines  the  character  of  the  soil  as  sandy, 
clay,  or  loam.  The  term  '  fine  earth '  is  used  to 
designate  that  part  of  a  soil  which  passes  through  a 
sieve  with  holes  0.5  mm.  (0.02  inch)  in  diameter. 
Coarse  sand  particles  and  rock  fragments  which  fail 
to  pass  through  the  sieve  are  called  skeleton.  The 
amounts  of  fine  earth  and  skeleton  are  variable.  Ara- 
ble soils,  in  general,  contain  from  5  to  20  per  cent,  of 
skeleton.  • 

The  fine  earth  is  composed  of  six  grades  of  soil 
particles.  The  names  and  sizes  are  as  follows  : 

Millimeters.  Inches. 

Medium  sand 0.5      to  0.25  0.02      to  o.oi 

Fine  sand 0.25    to  o.i  o.oi      to  0.004 

Very  fine  sand- ...   o.i      to  0.05  0.004    to  0.002 

Silt 0.05    to  o.oi  0.002    to  0.0004 

Fine  silt o.oi    to  0.005  0.0004  to  0.0002 

Clay 0.005  and  less  0.0002  and  less 

Soils  are  mechanical  mixtures  of  various-sized  par- 
ticles. In  most  soils  there  is  a  predominance  of  one 
grade,  as  clay  in  heavy  clay  soils,  and  medium  sand 
in  sandy  soils.  No  soil,  however,  is  composed  entirely 


12  SOILS   AND    FERTILIZERS 

of  one  grade.  The  clay  particles  are  exceedingly 
small  ;  it  would  take  5000  of  the  larger  ones,  if  laid 
in  a  line  with  the  edges  touching,  to  measure  an  inch, 
while  it  would  take  but  50  of  the  larger  medium  sand 
particles  to  measure  an  inch. 

5.  Clay. — The  term   clay  used   physically  denotes 
those  soil  particles  less  than  0.005  mm-  (0.0002  inch) 
in  diameter,  without  regard  to  chemical  composition. 
As  used  in  a  physical  sense  clay  may  be  silica,   feld- 
spar,  limestone,  mica,   kaolin,  or  any   other  rock   or 
mineral  which  has  been  pulverized  until  the  particles 
are  less  than  0.005  mm-  ^n   diameter.     Chemically, 
however,  the  term  clay  is  restricted  to  one  material, 
as  will  be  explained  in  another  part  of  the  work.  The 
physical  properties  of  clay  are  well  known.     It  has  the 
power  of  absorbing  a  large  amount  of  water,  and  will 
remain   suspended   in  water  for  a  long  time.     The 
roiled  appearance  of  many  streams  and  lakes  is  due  to 
the  presence  of  suspended  clay  particles.     The  amount 
in  agricultural  soils  may  range  from  3  to  50  per  cent. 
Clay  soils,  if  worked  when  too  wet,  become  puddled  ; 
then  percolation  cannot  take  place,  and   the  accumu- 
lated surface  water  must  be   removed   by   the  slow 
process  of  evaporation. 

6.  Silt. — Silt  particles  are,  in  size,  between  sand 
and  clay.     Many  of  the  western  prairie  subsoils,  clay- 
like  in  nature,  are  composed  mainly  of  silt.     The  silt 
imparts  characteristics  intermediate  to  sand  and  clay. 
While  a  clay  soil  is  nearly  impervious  to  water,  and 
when  wet  works  with  difficulty,  a  silt  soil  is  more  per- 
meable, but  is  not  as  open  and  porous  as  a  sandy  soil. 


SAND 


13 


When  a  soil  containing  large  amounts  of  clay  and  silt 
is  treated  with  water,  the  silt  settles  slowly,  while 
the  clay  remains  in  suspension.  The  fine  deposit  in 
ditches  and  drains,  where  the  water  moves  slowly,  is 
mainly  silt. 

7.  Sand. — There  are  three  grades  of  sand.     The 
characteristics,  as  permeability  and   non-cohesion  of 


Fig.  i.  Medium  sand  X  150.  Fig.  2.  Fine  sand  X  150-  Fig-  3- 
Very  fine  sand  X  150-  Fig.  4.  Silt  X  325.  Fig.  5.  Fine  silt  X 
325.  Fig.  6.  Clay  X  325. 

particles,  are  so  well  known  that  they  do  not  require 
discussion.  A  soil  composed  entirely  of  sand  would 
have  little,  if  any,  agricultural  value.  Sandy  soils 
usually  contain  from  5  to  15  per  cent,  of  clay  and 
silt.  The  relative  sizes  of  sand,  silt,  and  clay  are  given 
in  the  illustration. 


14  SOILS   AND   FERTILIZERS 

8.  Form  of  Soil  Particles, — Soil  particles  are  ex- 
tremely varied  in  form.  When  examined  with  the 
microscope  they  show  the  same  diversity  as  is  observed 
in  larger  stones.  In  some  soils  the  particles  are  spher- 
ical, while  in  others  they  are  angular.  The  shape  of 
the  particles  is  determined  by  the  way  in  which  the 
soil  has  been  formed,  and  also  by  the  nature  of  the 
rock  from  which  it  was  produced. 

The  form  and  arrangement  of  the  particles  are  im- 
portant factors  to  consider  in  dealing  with  the  water 
content  of  soils.  In  the  wheat  lands  of  the  Red  River 
Valley  of  the  North,  the  particles  are  small  and  spher- 
ical, being  formed  largely  from  limestone  rock,  while 
the  subsoil  of  the  western  prairie  regions  is  composed 
largely  of  angular  silt  particles,  which  are  intermingled 
with  clay,  forming  a  mass  containing  only  a  minimum 
of  inter  soil  spaces.  The  silt  particles  being  angular 
and  embedded  in  the  clay,  the  soil  has  more  the  char- 
acter of  clay  than  of  silt.  While  these  two  soils  are 
unlike  in  physical  composition,  the  form  and  arrange- 
ment of  the  particles  give  each  nearly  the  same  water- 
holding  power.  Two  soils  may  have  the  same  mechan- 
ical composition  and  yet  possess  materially  different 
physical  properties  because  of  a  difference  in  the  form 
and  arrangement  of  the  soil  particles.  In  some  soils 
10  per  cent,  of  clay  is  of  more  agricultural  value  than 
in  other  soils.  Ten  per  cent,  of  clay  associated  with 
60  or  70  per  cent,  of  silt  makes  a  good  grain  soil, 
while  10  per  cent,  of  clay  associated  largely  with  sand 
makes  a  soil  poorly  suited  to  grain  culture. 

The  classification  of  the  soil  particles  into  sand,  silt, 


SEPARATING   SOII,   PARTICLES  15 

and  clay  is  purely  an  arbitrary  one.  Various  authors 
use  these  terms  in  different  ways,  and  when  compar- 
ing soils  reported  in  different  works,  one  may  avoid 
confusion  by  omitting  the  names  and  noting  only  the 
sizes  of  the  particles.  A  division  has  recently  been 
suggested  by  Hopkins7,  in  which  the  square  root  of  ten 
is  taken  as  the  constant  ratio  between  the  grades  of 
soil  particles. 

9.  Number  of  Particles  per  Gram  of  Soil.— It  has 
been  estimated  that  a  gram  of  soil  contains  from 
2,000,000,000  to  20,000,000,000  soil  particles  ;  soils 
which  contain  less  than  1,700,000,000  are  unproduc- 
tive. The  number  of  particles  in  a  given  volume  of 
soil  varies  with  their  size  and  form.  According  to 
Whitney8  the  number  of  particles  per  gram  of  differ- 
ent soil  types  is  as  follows  : 

Early  truck 1,955,000,000* 

Truck  and  small  fruit 3,955,000,000 

Tobacco 6,786,000,000 

Wheat 10,228,000,000 

Grass  and  wheat 14,735,000,000 

Limestone 19,638,000,000 

Assuming  that  the  particles  are  all  spheres,  it  is  es- 
timated that  in  a  cubic  foot  of  soil  a  surface  area  of 
from  two  to  three  and  one-half  acres  is  presented  to 
the  action  of  the  roots. 

i  o .  Methods  Employed  in  Separating  Soil  Particles . 
— Sieves  with  circular  holes  0.5,  0.25  and  o.i  mm. 
are  employed  for  the  purpose  of  separating  the  three 
coarser  grades  of  sand.  The  sieve  a,  0.5  mm.  size,  is  con- 


*  Figures  below  sixth  place  omitted  and  cyphers  substituted. 


i6 


SOILS   AND    FERTILIZERS 


nected  with  the  filtering  flask  c  by  means  of  the  tube 
l>,  and  the  flask  is  connected  at  point  d  with  a  suction- 
pump.  Ten  grams  of  soil,  after  soft  pestling  with 
boiling  water,  are  placed  in  the  sieve.  Water  is  passed 
through  until  the  washings  are  clear.  All  particles 
larger  than  0.5  mm.  remain  in  the  sieve  and,  after  dry- 
ing and  igniting,  are  weighed.  The  contents  of  flask  c, 
containing  the  particles  less  than  0.5  mm.  are  then 
passed  through  a  sieve  having  holes  0.25  mm.  in 
diameter.  Finally  a  o.io  mm.  diameter  sieve  is  used. 

The  fine  sand  and  silt  are  separated  by  gravity.  The 
fine  sand  with  some  silt  and  clay  are  read- 
ily deposited  and  the  water  containing 
the  suspended  clay  is  decanted  into  a 
second  glass  vessel.  The  residue  is  treated 
with  more  water  and  allowed  to  settle ; 
this  operation  is  repeated  until  the  micro- 
scope shows  the  soil  particles  to  be  nearly 
all  of  one  grade.  The  separation  of  silt 
and  clay  is  facilitated 
by  the  use  of  a  centrifu- 
gal.9 

The  clay  is  obtained  Figs.  8  and  9. 
by  evaporating  an  aliquot  portion  of  the  washings  or 
by  determining  the  total  per  cent,  of  the  other  grades 
of  particles  and  the  volatile  matter  and  subtracting 
the  sum  from  100.  This  is  the  modified  Osborne  sed- 
imentation method.10 

Hilgard's  elutriator"   is  a  valuable  apparatus  for 
separating  the  soil  particles. 


SOIL  TYPES 

11.  Crop  Growth  and  Physical  Properties. — The 

preference  of  certain  crops  for  particular  kinds  of  soil, 
as  wheat  for  a  clay  subsoil,  potatoes  for  a  sandy  soil, 
and  corn  for  a  silt  soil,  is  due  mainly  to  the  peculiari- 
ties of  the  crop  in  requiring  definite  amounts  of  water, 
and  a  certain  temperature  for  growth.  These  condi- 
tions are  met  by  the  soil  being  composed  of  various 
grades  of  particles  which  enable  a  certain  amount  of 
water  to  be  retained,  and  the  soil  to  properly  respond 
to  the  influences  of  heat  and  cold.  In  considering 
soil  types,  it  should  be  remembered  that  there  are  so 
many  conditions  influencing  crop  growth  that  the 
crop-producing  power  cannot  always  be  determined  by 
a  mechanical  analysis  of  the  soil.  The  following 
types  have  been  found  to  hold  true  in  a  large  number 
of  cases  under  average  conditions,  but  they  do  not 
represent  what  might  be  true  of  a  case  under  special 
conditions.  For  example,  a  sandy  soil  of  good  fer- 
tility in  which  the  bottom  water  is  only  a  few  feet 
from  the  surface,  may  produce  larger  grain  crops  than 
a  clay  soil  in  which  the  bottom  water  is  at  a  greater 
depth.  In  judging  the  character  of  a  soil,  special 
conditions  must  always  be  taken  into  consideration. 
In  discussing  the  following  soil  types,  a  normal  supply 
of  plant  food  and  an  average  rainfall  are  assumed  in 
all  cases. 

12.  Potato   and  Early    Truck  Soils.— The  better 
types  of  potato  soils  are  those  which  contain  about  60 

.   per  cent,  of  medium  sand,  20  to  25  per  cent,  of  silt,  and 

(2) 


1 8  SOILS   AND   FERTILIZERS 

about  5  per  cent,  of  clay.  Soils  of  this  nature  when 
supplied  with  about  3  per  cent,  of  organic  matter  will 
contain  from  5  to  12  per  cent,  of  water.  The  best 
conditions  for  crop  growth  exist  when  the  soil  con- 
tains about  8  per  cent,  of  water.  In  a  sandy  soil, 
vegetation  may  reduce  the  water  to  a  much  lower 
point  than  in  a  clay  soil.  On  account  of  sandy  soil 
giving  up  its  water  so  readily  to  growing  crops  nearly 
all  is  available,  while  on  heavy  clay,  crops  show  the 
want  of  water  when  the  soil  contains  from  7  to  8  per 
cent,  because  the  clay  holds  the  water  so  tenaciously. 
When  potatoes  are  grown  on  soils  where  there  is  an 
abnormal  amount  of  water  the  crop  is  slow  in  matur- 
ing. For  early  truck  purposes  in  northern  latitudes, 
sandy  soils  are  the  most  suitable  because  they  warm 
up  more  readily,  and  the  absence  of  an  abnormal 
amount  of  water  results  in  early  maturity.  Excellent 
crops  of  potatoes  are  grown  on  many  of  the  silt  soils 
of  the  west  which  have  a  materially  different  com- 
position from  the  type  given.  A  soil  may  have  all 
of  the  requisites  physically  for  the  production  of  good 
potato  and  truck  crops,  and  still  be  unproductive  on 
account  of  unbalanced  chemical  composition  or  lack 
of  plant  food. 

13.  General  Truck  and  Fruit  Soils. — For  fruit  grow- 
ing and  general  truck  purposes  the  soil  should  contain 
more  clay  and  less  sand  than  for  early  truck  farming. 
Soils  containing  from  10  to  15  per  cent,  of  clay  and 
not  more  than  50  per  cent,  of  sand  are  best  suited  for 
growing  small  fruits.  Such  soils  will  retain  from  10 
to  1 8  per  cent,  of  water.  There  is  a  noticeable  differ- 


MEDIUM    GRASS   AND    GRAIN   SOILS  1 9 

ence  as  to  the  adaptability  of  different  kinds  of  fruit 
to  different  soils.  Some  fruits  thrive  on  clay  land, 
provided  the  proper  cultivation  and  treatment  are 
given.  There  is  as  much  diversity  of  soil  required  for 
producing  different  fruit  crops  as  for  the  production  of 
different  farm  crops.  As  a  rule,  however,  a  silt  soil  is 
most  capable  of  being  adapted  to  the  various  conditions 
required  by  fruit  crops. 

14.  Corn  Soils. — The  strongest  types  of  corn  soils 
are  those   which  contain   from    40  to  45   per  cent,  of 
medium  and  fine  sand  and  about  15  per  cent,  of  clay. 
Corn  lands  should  contain  about  15  per  cent,  of  avail- 
able water.     Heavy  clays  require  more  cultivation  and 
produce  corn   crops   which   mature  later  than  those 
grown  on  soils  not  so  close  in  texture.     Many  corn 
soils  contain  less  sand  and  clay,  but  more  silt  than  the 
figures  given.     If  a  soil   contains  a  high  per  cent,  of 
neutral  organic  matter,  good  corn  crops  may  be  pro- 
duced  where  there  is  less  than  12   per  cent,  of  clay. 
Soils  containing  a  high   per  cent,  of  sand  are  usually 
too  deficient  in  available  water  to  produce  a  good  corn 
crop.     On  the  other  hand,  heavy  clay  soils  are  slow  in 
warming  up  and  are  not  suited  to  corn  culture. 

The  best  types  of  corn  soils  have  the  necessary 
mechanical  composition  for  the  production  of  good 
crops  of  sorghum,  cotton,  flax,  and  sugar-beets.  How- 
ever, the  amount  of  available  plant  food  required  for 
each  crop  is  not  the  same.  The  western  prairie  soils, 
which  produce  most  of  the  corn  raised  in  the  United 
States,  are  composed  largely  of  silt. 

15.  Medium  Grass  and  Grain  Soils. — For  the  pro- 


20  SOILS   AND   FERTILIZERS 

duction  of  grass  and  grain  a  larger  amount  of  water 
is  required  than  for  corn.  The  yield  is  determined 
largely  by  the  amount  of  water  which  the  soil  con- 
tains. For  an  average  rainfall  of  about  30  inches, 
good  grass  and  grain  soils  should  contain  about  15  per 
cent,  of  clay  and  60  per  cent,  of  silt.  Such  a  soil 
ordinarily  holds  from  18  to  20  per  cent,  of  water. 
Many  grass  and  grain  soils  have  less  silt  and  more 
clay.  A  soil  composed  of  about  30  per  cent,  each  of 
fine  sand,  silt,  and  clay,  would  also  be  suitable,  me- 
chanically, for  general  grain  production.  There  are 
a  number  of  different  types  of  grass  and  grain  soils, 
with  different  proportional  amounts  of  sand,  silt,  and 
clay.  Silt  soils,  however,  form  the  larger  part  of  the 
grain  soils  of  the  United  States. 

16.  Wheat  Soils. —  For  wheat  production,  soils  of 
closer  texture  are  required  than  for  other  small  grains. 
There  are  three  classes  of  wheat  soils.  The  first  (i 
in  Fig.  10)  contains  from  30  to  50  per  cent,  of  clay 
particles,  these  being  mostly  disintegrated  limestone. 
The  soil  of  the  Red  River  Valley  of  the  North  belongs 
to  the  first  class.  The  surface  soil  contains  from  8  to 
12  per  cent,  of  vegetable  matter  and  the  subsoil  about 
25  per  cent,  of  limestone  in  a  very  fine  state  of  division. 
For  the  production  of  wheat,  the  subsoil  should  con- 
tain 20  per  cent,  of  water.  A  crop  can,  however,  be 
produced  with  less  water,  but  a  smaller  yield  is  ob- 
tained. 

The  second  type  of  wheat  soil  (2  in  Fig.  10)  con- 
tains less  clay  and  more  silt.  Many  prairie  subsoils 
which  produce  good  crops  of  wheat  contain  about  20 


WHEAT  SOILS 


21 


per  cent,  of  sand,  50  per  cent,  of  silt,  and  from  20  to 
30  per  cent,  of  clay.  Soils  of  this  class  when  well 
stocked  with  moisture  in  the  spring  are  capable  of 
producing  good  crops  of  wheat,  but  are  not  able  to 
withstand  drought  so  well  as  soils  of  the  first  class ; 
during  wet  seasons,  however,  they  produce  larger 
yields  than  heavier  clay  soils. 

1834 


Fig.  10.     Soil  types. 

i.  Heavy  wheat  soil.      2.  Average  wheat  soil.      3.  Medium  wheat 
and  grain  soil.     4.  Corn  soil. 

To  the  third  class  of  wheat  soils  (3  in  Fig.  10)  be- 
long those  which  are  composed  mainly  of  silt,  contain- 
ing usually  75  per  cent.,  and  from  10  to  15  per  cent,  of 
clay.  The  high  per  cent,  of  fine  silt  gives  the  soil 
clay-like  properties.  Soils  of  this  class  are  adapted  to 
a  great  variety  of  crops.  For  the  production  of  wheat 


22  SOILS   AND   FERTILIZERS 

on  silt  soils,  it  is  essential  that  a  good  supply  of 
organic  matter  be  kept  in  the  soil  so  as  to  bind 
the  soil  particles.  The  special  peculiarities  of  the 
different  grain  crops  as  to  soil  requirements  are  con- 
sidered in  connection  with  the  food  requirements  of 
crops. 

17.  Sandy,    Clay,   and   Loam   Soils. — In  ordinary 
agricultural   literature,   the   term   l  sandy,'   *  clay,'   or 
'  loam  '  is  used  to  designate  the  prevailing  character  of 
the  soil.     Sandy  soils  usually  contain  90  per  cent,  or 
more  of  silica  or  chemically  pure  sand.     The  term 
light  sandy  soil   is  sometimes  used  to  indicate  that 
the  soil  is  easily  worked,  while  the  term  heavy  clay 
means  that  the  soil  offers  great  resistance  to  cultiva- 
tion.    Many  soils  which  are  clay-like  in  character  are 
not  composed  very  largely  of  clay.     They  are  sub- 
soils in  the  western  states  which  have  clay -like  char- 
acteristics but  contain  only  about  15  percent,  of  clay, 
the  larger  part  of  the  soil  being  silt.     A  loam  soil  is  a 
mixture  of  sand  and   clay ;  if  clay  predominates  the 
soil  is  a  clay  loam,  while  if  sand  predominates  it  is  a 
sandy  loam. 

RELATION   OF  THE  SOIL  TO  WATER 

18.  Amount   of  Water   Required  by  Crops. — Ex- 
periments have  shown  that  it  takes  from  275  to  375 
pounds  of  water  to  produce  a  pound  of  dry  matter  in 
a  grain  crop.     In  order  to  produce  an  average  acre  of 
wheat,  350  tons  of  water  are  needed.     The  amount  of 
water  required  for  the  production  of  an  average  acre 
of  various  crops  is  as  follows  : I2 


BOTTOM   WATER  23 

Average  amount.        Minimum  amount. 
Tons  water.  Tons  water. 

Clover ••  400                           310 

Potatoes 400                           325 

Wheat 350                           300 

Oats 375                           3oo 

Peas -. 375                           3°° 

Corn 300 

Grapes 375 

Sunflowers6 6000 

The  rainfall  during  the  time  of  growth  is  frequently 
less  than  the  amount  of  water  required  for  the  pro- 
duction of  a  crop.  One  inch  of  rainfall  is  equal  to 
about  90  tons  per  acre.  An  average  rainfall  of  2 
inches  per  month  during  the  three  months  of  crop 
growth  is  equivalent  to  only  540  tons  of  water  per 
acre,  a  large  part  of  which  is  lost  by  evaporation. 
Hence  it  is  that  the  rainfall  during  an  average  grow- 
ing season  is  less  than  the  amount  of  water  required 
to  produce  crops,  and  hence  the  water  stored  up  in  the 
subsoil  must  be  drawn  upon  to  a  considerable  extent. 
Inasmuch  as  the  soil's  reserve  supply  of  water  is  such 
an  important  factor  in  crop  production,  it  follows  that 
the  capacity  of  the  subsoil  for  storing  and  supplying 
water  as  needed  is  a  matter  of  much  importance,  par- 
ticularly since  the  power  of  the  soil  for  absorbing 
and  retaining  water  may  be  influenced  by  cultivation 
and  manuring.  Before  discussing  the  influence  of 
cultivation  upon  the  soil  water,  the  forms  in  which  it 
is  present  in  the  soil  should  be  studied.  Water  is 
present  in  soils  in  three  forms  :  (i)  bottom  water,  (2) 
capillary  water,  and  (3)  hydroscopic  water. 

19.  Bottom  Water  is  water  which  stands  in  the  soil 


24  SOILS   AND    FERTILIZERS 

at  a  general  level,  and  fills  all  the  spaces  between  the 
soil  particles.  Its  distance  from  the  surface  can  be 
told  in  a  general  way  by  the  depth  of  surface  wells. 
Bottom  water  is  of  service  to  growing  crops  when  it  is 
at  such  a  depth  that  it  can  be  brought  to  the  plant 
roots  by  capillarity,  but  when  too  near  the  surface  so 
that  the  roots  are  immersed,  very  poor  conditions  for 
crop  growth  exist.  When  the  bottom  water  can  be 
brought  within  reach  of  the  roots  by  capillarity,  a  crop 
has  an  almost  inexhaustible  supply.  In  many  soils 
known  as  old  lake  bottoms,  such  conditions  exist. 


Fig.  ii.     Water  films  surrounding  soil  particles. 

20.  Capillary  Water.  —  The  water  held  in  the 
minute  spaces  above  the  bottom  water  is  known  as  the 
capillary  water.  The  capillary  spaces  of  the  soil  are 
the  small  spaces  between  the  soil  particles  in  which 
water  is  held  by  surface-tension  ;  that  is,  the  force 
acting  between  the  soil  and  the  water  is  greater  than 
the  force  of  gravity.  If  a  series  of  glass  tubes  of  dif- 
ferent diameters  be  placed  in  water  it  will  be  observed 
that  in  the  smaller  tubes  water  rises  much  higher  than 
in  the  larger.  The  water  rises  in  all  of  the  tubes 
until  a  point  is  reached  where  the  force  of  gravity  is 
equal  to  the  force  of  surface-tension.  In  the  smaller 
tubes  surface-tension  is  greater  than  the  force  of 


CAPILLARY   WATER 


gravity,  and  the  water  is  drawn  np  into  the  tube.  In 
the  larger  tubes  the  surface-tension  is  less  and  water 
is  raised  only  a  short  distance.  There  are  present  in 
the  soil  many  spaces  which  are  capable  of  taking 
up  water  in  the  same  way  as  the  small  glass  tubes. 
The  height  to  which-  water  can  be  raised  by  capillarity 
depends  upon  the  size  and  arrangement  of  the  soil 
particles.  Water  may  be  raised  by  capillarity  to  a 
height  of  several  feet.  Ordinarily,  however,  the  capil- 
lary action  of  water  is  confined  to  a  few  feet.  The 


Fig.  12.     Comparative  height  to  which  water  rises  in  glass  tubes. 

arrangement  of  the  soil  particles  influences  greatly  the 
capillary  power  of  the  soil.  Usually  from  30  to  60  per 
cent,  of  the  bulk  of  a  soil  is  air  space  ;  by  compacting, 
the  air  spaces  are  decreased  ;  by  stirring,  the  air  spaces 
are  increased.  In  soils  of  a  close  texture,  as  heavy 
clays,  an  increase  in  air  spaces  results  in  an  increase  of 
capillary  spaces  and  of  water-holding  capacity,  while 
in  other  soils,  as  coarse  sandy  soils,  increasing  the  air 
spaces  decreases  the  capillary  spaces  and  the  water- 
holding  capacity.  The  best  conditions  for  crop  pro- 
duction exist  when  the  soil  contains  water  to  the  extent 
of  about  40  per  cent,  of  its  total  capacity  of  saturation. 


26  SOILS   AND   FERTILIZERS 

21.  Hydroscopic  Water, — By  hydroscopic  water  is 
meant  the  water  content  of  the  soil  absorbed  from  the 
atmosphere.     The  air  which  occupies  the  non-capillary 
spaces  of  the  soil  is  charged  with  moisture  in  propor- 
tion to  the  water  in  the  soil.     Under  normal  condi- 
tions the  soil  atmosphere  is  nearly  saturated.     When 
soils  have  exhausted  their  capillary  water,  the  water 
in   the  soil   atmosphere  is   correspondingly   reduced. 
The  available  supply  in  other  forms  being  exhausted, 
the    hydroscopic    water   cannot    contribute    to    plant 
growth   unless  the  soil  is  supplied  with  hydroscopic 
water  from  heavy  fogs. 

22.  Loss  of  Water  by  Percolation. — Whenever  a 
soil  becomes  saturated,  percolation  or  a    downward 
movement  of  the  water  begins.     The  extent  to  which 
losses  by  percolation  may  occur  depends  upon  the 
character   of    the    soil    and    the    amount    of   rainfall. 
When  soils  are  covered  with  vegetation,  the  losses  by 
percolation  are  less  than  from   barren  fields.     In  all 
soils  which  have  only  a  limited  number  of  capillary 
spaces  and  a  large  number  of  non-capillary  spaces,  the 
amount  of  water  which  can  be  held  above  the  bottom 
water  is  small.     From  such  soils  the  losses  by  perco- 
lation are  greater  than  from  soils  which  have  a  larger 
number  of  capillary  spaces,  and  a  smaller  number  of 
non-capillary  spaces.     In  coarse  sandy  soils  many  of 
the  spaces  are  too  large  to  be  capillary. 

If  all  of  the  water  which  falls  on  some  soils  could  be 
retained  and  not  carried  beyond  the  reach  of  crops  by 
percolation,  there  would  be  an  ample  supply  for  agri- 
cultural purposes.  To  prevent  losses  by  percolation, 


LOSS   OF   WATER    BY   EVAPORATION  27 

the  texture  of  the  soil  may  be  changed  by  cultivation 
and  by  the  use  of  manures.  If  the  soil  is  of  very  fine 
texture,  as  a  heavy  clay,  percolation  is  slow,  and  before 
the  water  has  time  to  sink  into  the  soil,  evaporation 
begins ;  with  good  cultivation,  the  water  is  able  to 
penetrate  to  a  depth -beyond  the  immediate  influence 
of  evaporation.  Compacting  an  open  porous  soil  by 
rolling,  checks  rapid  percolation  and  prevents  the 
water  from  being  carried  beyond  the  reach  of  plant 
roots.  In  order  to  prevent  excessive  losses  by  perco- 
lation, the  management  must  be  varied  to  suit  the  re- 
quirements of  different  soils.  In  regions  of  heavy 
rainfall  and  mild  winters  the  losses  of  both  water  and 
plant  food  by  percolation  are  often  large. 

23.  Loss  of  Water  by  Evaporation. — The  factors 
which  influence  evaporation  are  temperature,  humid- 
ity, and  rate  of  movement  of  the  air.  When  the  air 
contains  but  little  moisture  and  is  heated  and  moving 
rapidly,  the  most  favorable  conditions  for  evaporation 
exist.  In  semiarid  regions  the  losses  of  water  by 
evaporation  are  much  greater  than  by  percolation. 
The  dry  air  comes  in  contact  with  the  soil,  the  soil 
atmosphere  gives  up  its  water,  which  has  been  taken 
from  the  soil,  and,  unless  checked  by  cultivation,  the 
subsoil  water  is  brought  to  the  surface  by  capil- 
larity and  lost.  In  porous  soils,  a  greater  free- 
dom of  movement  of  the  air  is  possible,  which 
increases  the  rate  of  evaporation.  When  the  sur- 
face of  the  soil  is  covered  with  a  layer  of  finely 
pulverized  earth,  or  with  a  mulch,  excessive  losses 
by  evaporation  cannot  take  place,  because  a  material 


28  SOILS   AND   FERTILIZERS 

of  different  texture  is  interposed  between  the  soil  and 
the  air. 

24.  Loss  of  Water   by  Transpiration. —  Losses  of 
water  may  also  occur  from  the  leaves  of  plants  by  the 
process  known  as  transpiration.     Helriegel  observed 
that  during  some  years  100  pounds  more  water  were 
required  to  produce  a  pound  of  dry  matter  than  in 
other  years,  because  of  the  difference  in  the  amount  of 
water   lost  by  transpiration.     The  loss  of    water  by 
evaporation  can  be  controlled  by  cultivation,  but  the 
loss  by  transpiration  can  be  only  indirectly  influenced. 
Hot,  dry  winds  may  cause  crops  to  wilt  because  the 
water  lost  by  transpiration  exceeds  the  amount  which 
the  plant  takes  from  the  soil. 

25.  Drainage. — Good  drainage  is  essential  in  order 
to  properly  regulate  the  water  supply.     An  excessive 
amount  of  water  in  the  soil  is  equally  as  injurious  as 
a  scant  amount.     If  the  water  which  falls  on  the  land 
is  allowed  to  flow  over  the  surface  and  is  not  retained 
in  the  soil,  there  is  not  sufficient  reserve  water  for 
crop  growth.     The  object  of  good  drainage  is  to  store 
as  much  water  as  possible  in  the  subsoil  and  to  pre- 
vent surface  accumulation  and  loss.     Good  drainage 
is  accomplished  by  thorough   cultivation,   and  in  re- 
gions of  heavy  rainfall,  by  tile  drainage.  Well-drained 
land  is  warmer  in  the  spring,   has  a  larger  reserve 
store  of  water,  and  is  in  better  condition   for  crop 
growth.     The  drainage  of  wet  and  low  lands  forms  an 
important  feature  of  rural  engineering.  Many  swampy 
lands  are  highly  productive  when  properly  drained. 


CAPILLARITY   INFLUENCED    BY   CULTIVATION          29 

The  reclamation  of  such  lands  is  briefly  considered  in 
Chapter  III. 

26.  Influence  of  Forest  Regions. — The  deforesting 
of  large  areas  near  the  sources  of  rivers  has  an  injurious 
influence  upon  the  moisture  content  of  adjoining  farm 
lands.     By  cutting  over  and  leaving  barren  large  tracts, 
less  water  is  retained  in  the  soil.     Near  forest  regions 
the  air  has  a  higher  moisture  content,    due   to   the 
water  given  off  by  evaporation.     Farm  lands  adjacent 
to  deforested   districts   lose    water   more   rapidly   by 
evaporation,  because  the  air  is  so  much  drier.     In 
Section  24  it  was  stated  that  losses  of  water  by  trans- 
piration could  be  indirectly  influenced.     This  can  be 
accomplished  by  retaining  our  forests. 

Good  drainage  is  necessary  not  only  for  individual 
farms,  but  also  for  an  entire  community.  Good  stor- 
age capacity  in  the  form  of  forest  lands,  for  the  surplus 
water  which  accumulates  near  the  sources  of  large 
rivers  is  also  a  necessity  to  agriculture. 

The  three  ways  in  which  crops  are  deprived  of 
water  are  by  (i)  percolation,  (2)  evaporation,  and  (3) 
transpiration.  With  proper  methods  of  cultivation 
losses  by  percolation  and  evaporation  may  be  controlled, 
and  losses  by  transpiration  may  be  reduced. 

INFLUENCE  OF  CULTIVATION  UPON   THE  WATER   SUPPLY 
OF   CROPS 

27.  Capillarity  Influenced  by  Cultivation.  —  The 

capillarity  of  the  soil  can  be  influenced  by  different 
methods  of  cultivation,  as  rolling  and  subsoiling,  deep 
plowing  and  shallow  surface  cultivation.  The  method 
of  cultivation  which  a  soil  should  receive  in  order  to 


30  SOILS   AND   FERTILIZERS 

secure  the  best  water  supply  for  crops  must  vary  with 
the  rainfall,  the  nature  of  the  soil,  and  the  crop  to  be 
produced.  It  frequently  happens  that  the  annual 
rainfall  is  sufficient  to  produce  good  crops,  but  is  too 
unevenly  distributed,  and  hence  is  not  all  utilized  to 
the  best  advantage.  It  is  possible,  to  a  great  extent, 
to  vary  the  cultivation  so  as  to  conserve  the  moisture 
of  the  soil  and  meet  the  requirements  of  crops. 

28.  Shallow  Surface  Cultivation. — When  shallow 
surface  cultivation  is  practiced,  the  capillary  spaces 


Fig.  13.     Soil  with  surface  cultivation. 

near  the  surface  are  destroyed  and  the  direct  connec- 
tion of  the  subsoil  water  with  the  surface  is  broken, 
a  layer  of  finely  pulverized  earth  covers  the  surface, 
and  the  soil  particles  have  been  disturbed  so  there 
is  not  that  close  contact  which  enables  the  water  to 
pass  from  particle  to  particle.  When  evaporation  takes 
place  there  is  a  movement  of  the  subsoil  water  to  the 
surface,  but  if  the  surface  is  covered  with  a  layer  of 
fine  earth  of  different  texture,  the  subsoil  water  can- 
not readily  pass  through  such  a  medium,  and  evapora- 
tion is  checked.  Hence  shallow  surface  cultivation 
conserves  the  soil  moisture. 

The  means  by  which  surface  cultivation  is  accom- 


SHALLOW   SURFACE   CULTIVATION  31 

published  must,  of  necessity,  vary  with  the  nature  of  the 
soil.  If  a  harrow  is  used,  the  pulverization  should  be 
complete.  If  a  disk  is  used,  the  teeth  should  be  set  at 
an  angle,  and  not  perpendicularly,  so  as  to  prevent,  as 
suggested  by  King,13  the  formation  of  hard  ridges 
which  hasten  evaporation.  When  the  disk  is  set  at  an 
angle,  a  layer  of  soil  is  completely  cut  off,  and  the 
capillary  connection  with  the  subsoil  is  broken.  Sur- 
face cultivation  should  be  from  two  to  three  inches 


Fig.  14.     Soil  without  surface  cultivation. 

deep,  and  the  finer  the  condition  in  which  the  surface 
soil  is  left  the  better. 

Shallow  surface  cultivation  is  an  effectual  means  of 
conserving  soil  moisture.  It  can  be  practiced  in  con- 
nection with  deep  plowing,  shallow  plowing,  subsoil- 
ing,  or  rolling  ;  in  fact,  it  can  be  combined  with  any 
method  of  treating  the  land.  Shallow  surface  cultiva- 
tion does  not  mean  that  the  soil  should  not  be  pre- 
viously well  prepared  by  thorough  cultivation.  The 
following  example  shows  the  extent  to  which  shallow 
surface  cultivation  may  conserve  the  soil  water.14 

Per  cent,  of  water  in  cornfield. 


With  shallow  sur- 
face cultivation. 


Soil,  depth  3  to  9  inches 14.12 

Soil,  depth  9  to  15  inches 17.21 


Without  shallow 
surface  cultivation. 

8.02 
12.38 


32  SOILS   AND   FERTILIZERS 

29.  Cultivation  After  a  Rain. — When  evaporation 
takes  place  immediately  after  a  rain,  not  only  is  there 
a  loss  of  the  water  which  has  fallen,  but  there  may 
also  be  a  loss  of  the  subsoil  water  by  translocation,  if 
nothing  be  done  to  prevent.13  The  following  example 
shows  the  extent  to  which,  the  subsoil  water  may  be 
brought  to  the  surface.14 

Per  cent,  of  water. 

Surface  soil.  Subsoil. 

I  to  3  inches.  6  to  12  inches. 

Before  the  shower 9.77  18.22 

After  the  shower 22.11  16.70 

The  rainfall  was  sufficient  to  have  raised  the  water 
content  of  the  surface  soil  to  20.77  per  cent.  The 
subsoil  showed  a  loss  of  1.52  per  cent,  while  the  sur- 
face soil  showed  a  gain  of  1.34  per  cent,  in  addition  to 
the  water  received  from  the  shower.  If  evaporation 
begins  before  the  equilibrium  is  reestablished,  there  is 
lost,  not  only  the  water  from  the  shower,  but  also  the 
water  which  has  been  translocated  from  the  subsoil  to 
the  surface.  Hence  the  importance  of  shallow  surface 
cultivation  immediately  after  a  rain. 

When  a  subsoil  contains  a  liberal  supply  of  water, 
and  the  surface  soil  a  minimum  amount,  there  is  after 
a  shower  a  movement  of  the  subsoil  water  to  the  sur- 
face. The  soil  particles  at  the  surface  are  surrounded 
with  films  of  water  which  thicken  at  the  expense  of 
the  subsoil  water.  Surface-tension  is  the  cause  of  this 
movement  of  the  water  to  the  surface,  and  under  the 
conditions  stated  it  is  temporarily  greater  than  the 
force  of  gravity. 

A  hard  thin  crust  should  never  be  allowed  to  form 


SUBSOILING  33 

after  a  rain,  because  it  hastens  losses  by  evaporation, 
while  a  soil  mulch  formed  by  surface  cultivation  has 
the  opposite  effect. 

30.  Rolling. — The  use  of   heavy  rollers  for  com- 
pacting the  soil  is  beneficial  in  a  dry  season  on  a  soil 
containing  large  proportions  of  sand  and  silt.   Rolling 
the  land  compacts  the  soil  and  improves  the  capillary 
condition,   enabling  more  of  the  subsoil  water  to  be 
brought   to   the   surface.     Experiments   have  shown 
that  when  land  is  rolled  the  amount  of  water  in  the 
surface  soil  is  increased.     This  increase  is,  however, 
at  the  expense  of  the  subsoil   water.13     Unless  rolled 
land  receives  surface  cultivation,  excessive  losses  by 
evaporation,  due  to  improved  capillarity,  may  result. 
The  use  of  the  roller  on  heavy  clay  land  during  a  wet 
season  results  unfavorably.     In  some  localities  rolling 
and  subsequent  surface  cultivation  are  not  admissible 
on  account  of  the  drifting  of  the  soil,  caused  by  heavy 
winds. 

31.  Subsoiling.  —  By  subsoiling  is  meant  pulveri- 
zing  of   the   soil   below  the   furrow   slice.     This   is 
accomplished   with   the  subsoil  plow,   which  simply 
loosens  the  soil  without  bringing  the  subsoil  to  the 
surface.     The  object  of  subsoiling  is   to  enable  the 
land  to  retain,  near  the  surface,  more  of  the  rainfall. 
Heavy  clay  lands  are  sometimes  improved  by  occasional 
subsoiling,  but  its  continued  practice  is  not  desirable. 
For  orcharding  and  fruit-growing,  it  is  frequently  re- 
sorted   to,   but   is  not  beneficial  on  soils  containing 
large  amounts  of  sand  and  silt.     Rolling  and  subsoil- 
ing are  directly  opposite  in  effect.     Soils  which  are 

(3) 


34  SOILS   AND   FERTILIZERS 

improved  by  rolling  are  not  improved  by  subsoiling. 
The  additional  expense  involved  should  be  considered 
when  subsoiling  is  to  be  resorted  to.  Experiments 
have  not  as  yet  been  sufficiently  decisive  to  indicate 
all  cf  the  conditions  most  favorable  for  this  practice. 

32.  Fall  Plowing  followed  by  surface  cultivation 
conserves  the  soil  water,  by  checking  evaporation  and 
leaving  the  land  in  better  condition  to  retain  moisture. 
If  conditions  allow,  fall  plowing  should  be  followed 
by  surface  cultivation.  In  some  localities  heavy  winds 
prevent  this  from  being  practiced.     Evaporation  may 
take  place  from  unplowed  land  during  the  fall,  and  in 
the  spring  the  soil  contain  appreciably  less  water  than 
plowed  land.     By  fall  plowing  it  is  possible  to   carry 
over  a  water  balance  in  the  soil  from  one  year  to  the 
next. 

33.  Spring  Plowing. — When  land  is  plowed  late  in 
the  spring  there  has  been  a  loss  of  water  by  evapora- 
tion, and  the  soil  has  not  been   able  to  store  up  as 
much  of  the  rain  and  snow  as  if  fall  plowing  had 
been  practiced.15     Dry  soil  is  plowed  under  and  moist 
soil  brought   to   the  surface.     If  surface   cultivation 
does  not  follow,  this  moisture  is  readily  lost  by  evapo- 
ration, good  capillary   connection  of  the  surface  soil 
and  subsoil  is  not  obtained,  and  the  furrow  slice  soon 
becomes  dry. 

Per  cent,  of  water  in14 


April  25th.  Fall  plowed  Spring  plowed 

land.  land. 

From  2  to    6  inches 24.7  22.4 

"     6  to  12      "       26.6  2\.i 

"    12  to  18      "       28.8  26.5 

Average  difference    2.37  per  cent. 


DEPTH    OF   PLOWING  35 

Surface  cultivation  should  immediately  follow  both 
spring  and  fall  plowing. 

34.  Mulching. — The  use  of  well-rotted  manure  or 
straw,   spread  over  the  surface  as  a  mulch,  prevents 
evaporation.     In    forests   the   leaves   form    a   mulch 
which  is  an  important  factor  in  maintaining  the  water 
supply.     In  order  that  a  mulch  be  effectual,  it  must 
be  compacted, — a  loose  pile  of  straw  is  not  a  mulch. 
In  reclaiming  lands  gullied  by  water,   mulching  is 
very  beneficial.      A  light  mulch  may  also  be  used  to 
encourage  the  growth  of  grass  on  a  refractory  hillside. 
When  land  is  mulched,  evaporation  is  checked.     Sur- 
face cultivation  and  mulching  may  be  advantageously 
combined.14 

Per  cent,  of  water  in 

Mulched  straw- 
berry patch.  Unmulched. 

Soil  2  to    5  inches 18.12  11.17 

"      6  to  12      "       22.18  18.14 

"    12  to  18      "       24.31  21.11 

35.  Depth  of  Plowing. — The  depth  to  which  a  soil 
should  be  plowed  in  order  to  give  the  best  results  must, 
of  necessity,  vary  with  the  conditions.     Deep  plowing 
of  sandy   land   is  not  advisable,   particularly   in  the 
spring.     On  clay  land  deeper  plowing  should  be  the 
rule.     The  longer  a  soil  is  cultivated  the  deeper  and 
more   thorough    should    be   the   cultivation.     While 
shallow  plowing  is  admissible  on  new  prairie  land, 
deeper  cultivation  should  be  practiced  when  the  land 
has   been    cropped  for  a  series  of  years.     Also,  the 
depth  of  plowing  should  be  regulated  by  the  season. 
In  the  prairie  regions,  and  in  the  northwestern  part  of 


36  SOILS   AND    FERTILIZERS  , 

the  United  States,  shallow  plowing  is  more  generally 
practiced  than  in  the  eastern  states.  Deep  plowing  in 
the  fall  gives  better  results  than  in  the  spring.  It  is 
not  a  wise  plan  to  plow  to  the  same  depth  every  year. 
Prof.  Roberts  says:16  "If  plowing  is  continued  at  one 
depth  for  several  seasons,  the  pressure  of  the  imple- 
ment and  the  trampling  of  the  horses  in  time  solidify 
the  bottom  of  the  furrow,  but  if  the  plowing  is  shallow 
in  the  spring  and  deep  in  summer  and  fall,  the  objec- 
tional  hard  pan  will  be  largely  prevented." 

In  regions  of  scant  rainfall  deep  plowing  of  silt  soils 
should  be  done  only  at  intervals  of  three  or  five  years. 
With  an  average  rainfall,  deep  plowing  should  be  the 
rule  on  soils  of  close  texture.  The  depth  of  plowing 
should  be  varied  to  meet  the  requirements  of  the  crop, 
of  the  soil  and  the  amount  of  rainfall. 

36.  Permeability  of  Soils.  —  The  rapidity  with 
which  water  sinks  into  the  soil  after  a  rain  depends 
upon  the  nature  of  the  soil,  and  upon  the  cultivation 
which  it  has  received.  Shallow  surface  cultivation 
leaves  the  soil  in  good  condition  to  absorb  water. 
When  the  surface  is  hard  and  dry  a  large  per  cent,  of 
the  water  which  falls  on  rolling  land  is  lost  by  sur- 
face drainage.  Soils  of  close  texture  which  contain 
but  few  non-capillary  spaces,  offer  the  greatest  resist- 
ance to  the  downward  movement  of  water. 

A  soil  is  permeable  when  it  is  of  such  a  texture  that 
it  does  not  allow  the  water  to  accumulate  and  clog 
the  non-capillary  spaces.  Cultivation  may  change 
the  tilth  of  even  a  clay  soil  to  such  an  extent  as  to 
render  it  permeable.  Deep  plowing  increases  per- 


FARM    MANURES  37 

meability.  In  regions  of  heavy  rains  increased  per- 
meability is  very  desirable  for  good  crop  production 
on  heavy  clays.  Sandy  and  loamy  soils  have  a  high 
degree  of  permeability,  and  it  is  not  necessary  that  it 
should  be  increased. 

37,  Fertilizers. — When  water  contains  dissolved 
salts,  it  is  more  susceptible  to  the  influence  of  surface- 
tension,  and  is  more  readily  brought  to  the  surface  of 


Fig.   15.     Sandy  soil  without  manure. 

the  soil.  In  commercial  fertilizers  soluble  salts  are 
present.  The  beneficial  effects  of  commercial  fertili- 
zers upon  the  moisture  content  of  soils  are  liable  to 
be  over-estimated,  because  the  fertilizer  undergoes  fix- 
ation when  applied,  and  does  not  remain  in  a  soluble 
condition.  Fertilizers  containing  soluble  salts  exercise 
a  favorable  influence  upon  the  moisture  content  of 
soils,  but  the  extent  of  this  influence  has  never  been 
determined  under  field  conditions. 

38.  Farm  Manures. — Well-prepared  farm  manures 
exercise  a  beneficial  effect  upon  the  moisture  content  of 
soils.  When  well-rotted  manure  is  worked  into  a  soil, 
the  coarse  soil  particles  and  masses  are  bound  together, 


SOILS   AND    FERTILIZERS 


and  the  non-capillary  spaces  are  made  capillary.  Free 
circulation  of  the  air,  which  increases  evaporation, 
is  prevented  when  a  sandy  soil  is  manured.  When 


Fig.  16.  Sandy  soil  with  manure. 

silt  and  sandy  soils  are  manured  they  are  capable  of 
retaining  more  water,  as  shown  by  the  following  ex- 
ample : I4 


Fine  sandy 

soil. 
Per  cent. 


Capacity  for  holding  water 25 


95  per  cent,  fine 

sandy  soil 

and  5  per 

cent,  manure. 

Per  cent. 

42 


The  manure  enables  the  soil  to  retain  more  water 
near  the  surface  and  prevents  losses  by  percolation. 
The  difference  in  moisture  content  between  manured 
and  unmanured  land  is  particularly  noticeable  in  a 
dry  season.14 


Sandy  soil 

well  manured. 

Water. 

Per  cent. 


Sandy  soil 
unmanured. 

Water. 

Per  cent. 


Soil  one  to  six  inches 10.50 


Coarse  leached  manure  may  have  just  the  opposite 
effect  by  producing  an  open  and  porous  condition  of 
the  soil. 


RELATION  OF  THE  SOIL  TO  HEAT 

39.  The  Sources  of  Heat  in  soils  are  (i)  solar 
heat,  and  (2)  heat  resulting  from  chemical  action. 
Solar  heat  is  the  main  source  for  crop  production. 
The  action  of  heat  upon  soils  has  been  studied  exten- 
sively by  Schiibler.  The  amount  of  heat  a  soil  is 
capable  of  absorbing  depends  upon  its  texture  and 
moisture  content.  All  dark-colored  soils  have  a 
greater  power  for  absorbing  heat  than  light-colored 
ones.  From  Schiibler's  experiments  it  appears  that 
when  dry,  there  may  be  as  great  a  difference  as  8°  C., 
between  light-  and  dark-colored  soils.  When  one  set 
of  soils  was  covered  with  a  thin  white  coat  of  mag- 
nesia, and  another  set  with  lampblack,  and  exposed 
under  like  conditions,  the  temperatures  were  :6 

White  coating.  Black  coating. 

Sand 43  50 

Gypsum 43  51 

Humus 42  49 

Clay 41  48 

L,oam 42  50 

The  presence  of  water  in  the  soil  modifies  the  power 
for  absorbing  heat.  A  sandy  soil  retains  about  12  per 
cent,  of  water,  while  a  humus  soil  retains  35  per  cent. 
The  additional  amount  of  water  in  the  humus  soil 
causes  the  soil  temperature  to  be  lower  than  that  of 
the  sandy  soil.  While  the  humus  soil  absorbs  more 
heat  than  the  sandy  soil,  the  heat  is  used  up  in  warm- 
ing the  water.  A  sandy  soil  readily  warms  up  in  the 
spring  on  account  of  the  relatively  small  amount  of 
water  which  it  contains. 


40  SOILS   AND   FERTILIZERS 

The  specific  heat  of  a  soil  is  the  amount  of  heat  re- 
quired to  raise  a  given  weight  i°  C.,  as  compared  with 
the  heat  required  to  raise  the  same  weight  of  water  i°. 
The  specific  heat  of  soils  ranges  from  0.2  to  0.4. 

The  effect  of  drainage  upon  soil  temperature  is 
marked.  The  surface  of  well-drained  land  is  usually 
several  degrees  warmer  than  that  of  poorly  drained 
land.  Water  being  a  poor  conductor  of  heat  it  follows 
that  soils  which  are  saturated  are  slow  to  warm  up  in 
the  spring.  At  a  depth  of  2  or  3  feet  there  is  not  such 
a  marked  difference  in  the  temperature  of  wet  and  dry 
soils.  It  is  to  be  observed  that  with  proper  systems  of 
drainage  the  surplus  water  is  removed  from  the  sur- 
face soil  and  stored  up  in  the  subsoil  for  the  future  use 
of  the  crop,  and  at  the  same  time  the  temperature  of  the 
surface  soil  is  raised,  thus  improving  the  conditions  for 
crop  growth.  The  relation  of  drainage  to  the  proper 
supply  of  water  and  temperature  for  crop  growth  is  a 
matter  which  generally  receives  too  little  consideration 
in  field  practice. 

40.  Heat  from  Chemical  Reactions  within  the 
Soil.— Heat  also  results  from  the  slow  oxidation  of 
the  organic  matter  of  the  soil.  When  organic  matter 
decomposes,  it  produces  heat.  A  load  of  nganure,  when 
it  rots  in  the  soil,  gives  off  the  same  amount  of  heat  as 
if  it  were  burned.  Manured  land  is  usually  i°  or  2° 
warmer  in  the  spring  than  unmanured  land ;  this  is 
due  to  the  oxidation  of  the  manure.  In  an  acre  of  rich 
prairie  soil  it  has  been  estimated  that  the  amount  of  or- 
ganic matter  which  undergoes  oxidation  produces  as 
much  heat  annually  as  would  be  produced  from  a  ton 


ORGANIC  MATTER  AND  IRON  COMPOUNDS     4! 

of  coal.17  In  well-drained  and  well-manured  land,  the 
additional  heat  is  an  important  factor  for  stimulating 
crop  growth,  particularly  in  a  cold,  backward  spring. 
The  production  of  heat  from  manure  is  utilized  in 
the  case  of  hotbeds  where  well-rotted  manure  is  covered 
with  soil ;  this  results  in  raising  the  temperature  of  the 
soil.  When  soils  are  well  manured,  heat  is  retained 
more  effectually.  In  case  of  early  frosts,  crops  on 
well-manured  land  will  often  escape. 

4.  Relation  of  Heat  to  Crop  Growth. — All  plant 
life  is  directly  dependent  upon  solar  heat  as  the  source 
of  energy  for  the  production  of  plant  tissue.  The 
heat  of  the  sun  is  the  main  force  at  the  plant's  dis- 
posal for  decomposing  water  and  carbon  dioxide  and 
for  producing  starch,  cellulose,  and  other  compounds- 
The  growth  of  crops  is  the  result  of  the  transformation 
of  solar  heat  into  chemical  energy  which  is  stored  up 
in  the  plant.  When  the  plant  is  used  for  fuel  or  for 
food  the  quantity  of  heat  produced  by  complete  oxida- 
tion is  equal  to  the  amount  of  heat  required  for  the 
formation  of  the  plant's  tissues. 

COLOR  OF  SOILS 

42.  Organic  Matter  and  Iron  Compounds.  —  The 

principal  materials  which  impart  color  to  soils  are  or- 
ganic matter  and  iron  compounds.  Soils  containing 
large  amounts  of  organic  matter  are  dark-colored. 
A  union  of  the  decaying  organic  matter  with  the 
mineral  matter  of  the  soil  produces  compounds  brown 
or  black  in  color.  When  moist,  many  soils  are  darker 
than  when  dry,  and  soils  in  which  the  organic  matter 


42  SOILS   AND   FERTILIZERS 

has  been  kept  up  by  the  use  of  manures  are  darker 
than  unmanured  soils.18  When  rich,  black,  prairie 
soils  lose  their  organic  matter  through  improper 
methods  of  cultivation,  or  when  the  organic  matter 
(humus)  is  extracted  in  chemical  analysis  the  soils 
become  light-colored. 

The  red  color*  of  soils  is  imparted  by  ferric  oxide, 
the  yellow,  by  smaller  amounts  of  the  same  material. 
A  greenish  tinge  is  supposed  to  be  due  to  the  pres- 
ence of  ferrous  compounds,  such  soils  being  so  close  in 
texture  as  to  prevent  the  oxidizing  action  of  the  air. 
Color  may  serve,  to  a  slight  extent,  as  an  index  of  fer- 
tility. Black  and  yellow  soils  are,  as  a  rule,  the  most 
productive.  The  main  reason  why  black  soils  are  so 
generally  fertile  is  because  they  contain  a  higher  per 
cent,  of  nitrogen.  Black  soils  are  occasionally  unpro- 
ductive because  of  the  presence  of  compounds  injurious 
to  vegetation. 

43.  Odor  and  Taste  of  Soils.— Soils  containing 
liberal  amounts  of  organic  matter  have  characteristic 
odors.  The  odoriferous  properties  of  a  soil  are  due  to 
the  presence  of  aromatic  bodies  produced  by  the  de- 
composition of  organic  matter.  In  cultivated  soils 
these  bodies  have  a  neutral  reaction.  Poorly  drained 
peaty  soils  give  off  volatile  acid  compounds  when 
dried.  The  amount  of  aromatic  compounds  in  soils 
is  very  small. 

The  taste  of  soils  varies  with  the  chemical  compo- 
sition. Poorly  drained  peaty  soils  usually  have  a 
slightly  sour  taste,  due  to  the  presence  of  organic 


RELATION   OF   SOILS   TO    ELECTRICITY  43 

acids.  Alkaline  soils  have  variable  tastes  according  to 
the  prevailing  alkaline  compound.  The  taste  of  a 
soil  frequently  reveals  a  fault,  as  acfdity  or  alkalinity. 

44.  Power  of  Soils  to  Absorb  Gases. — All  soils  pos- 
sess,  to   a  variable  extent,   the   power  of   absorbing 
gases.  When  decomposing  animal  or  vegetable  matter 
is  mixed  with  soil,  the  gaseous  products  given  off  are 
absorbed.     Absorption  is  the  result  of  both  chemical 
and  physical  action.       The  chemical  changes  which 
occur,  as  the  fixation  of  ammonia,   are  considered  in 
the  chapter  on  fixation.     The  organic  matter  of  the 
soil  is  the  principal  agent  in  the  physical  absorption  of 
gases  ;  peat  has  the  power  of  absorbing  large  amounts. 
This  action  is  similar  to  that  of  a  charcoal  filter  in 
removing  noxious  gases  from  water. 

45.  Relation  of  Soils  to  Electricity. — There  is  al- 
ways a  certain  amount  of  electricity  in  both  the  soil 
and  the  air.    The  part  which  it  takes  in  plant  growth 
is  not  well  understood.     The  action  of  a  strong  cur- 
rent upon  the  soil  undoubtedly  results  in  a  change  in 
chemical  composition,    but   in   order   to   change    the 
composition  of  the  soil  so  as  to  render  the  unavailable 
plant  food  available,  would  require  a  current  destruc- 
tive to  vegetation.      When  plants  are  subjected  to  too 
strong  a  current  of  electricity,  they  wilt  and  have  all 
of  the  after-effects  of  frost.  A  feeble  current  has  either 
an  indifferent  or  a  slightly  beneficial  effect  upon  crop 
growth.  The  slightly  beneficial  action  is  not  sufficient, 
however,  to  warrant  its  use  as  yet  in  general  crop  pro- 
duction on  account  of  cost.     The  action  of  a  weak 


44  SOILS   AND   FERTILIZERS 

current  of  electricity  is  undoubtedly  physiological 
rather  than  chemical,  unless  it  be  in  the  slighty  favor- 
able influence  which  it  exerts  upon  nitrification.  The 
electrical  conductivity  of  soils  has  been  taken  by  Whit- 
ney as  the  basis  for  the  determination  of  moisture  ; I9 
the  conductivity  of  a  soil,  however,  is  dependent 
largely  upon  the  nature  and  amount  of  dissolved  salts. 

46.  Importance  of  the  Physical  Study  of  Soils, — 

From  what  has  been  said  regarding  the  physical  prop- 
erties of  soils  it  is  evident  that  such  a  study  will  give 
much  valuable  information  regarding  their  probable 
agricultural  value.  While  the  physical  properties 
should  always  be  taken  into  consideration,  they  should 
not  form  the  sole  basis  for  judging  the  character  of  a 
soil,  because  two  soils  from  the  same  locality  frequently 
have  the  same  general  physical  composition  and  still 
have  entirely  different  crop-producing  powers,  due  to 
differences  in  chemical  composition  and  amounts  of 
available  plant  food. 

Attempts  have  been  made  to  over-estimate  the  value 
of  the  physical  properties  of  soils  and  to  explain  nearly 
all  soil  phenomena  on  the  basis  of  soil  physics.  Im- 
portant as  are  the  physical  properties  of  a  soil,  it  can- 
not be  said  that  they  are  of  more  importance  than  the 
chemical  or  other  properties.  In  fact  the  four  sciences, 
chemistry,  physics,  geology,  and  bacteriology,  are  all 
closely  connected  and  each  contributes  its  part  to  our 
knowledge  of  soils. 


CHAPTER  II 

GEOLOGICAL  FORMATION  AND   CLASSIFICATION   OF   SOILS 

47.  Agricultural  Geology. — The  geological  study 
of  a  soil  concerns  itself  with  the  past  history  of  that 
soil;  the  materials  out  of  which  it  has  been  produced, 
together  with  the  agencies  which  have  taken  a  part  in 
its  formation  and  distribution.     Geologically,  soils  are 
classified  according  to  the  period  in  the  earth's  history 
when   formed,    and    also    according   to   the  agencies 
which  have  distributed  them.       The  principles  of  soil 
formation  and  soil  distribution  should  be    understood, 
because  they  have  such  an  important  bearing  upon 
soil  fertility.     Agricultural   geology    is    of    itself    a 
separate  branch  of  agricultural  science.    In  this  work, 
only  a  few  of  the  topics  which  are  of  most  importance 
in  agriculture  are  treated  and  only  in  a  general  way. 

48.  Formation  of  Soils. — Geologists  state  that  the 
surface  of  the  earth  was  at  one  time  solid  rock.      It  is 
now  held  that  soils  have  been  formed   from   rock  by 
the  joint  action  of  the  various  agents  :     ( i)   heat  and 
cold,   (2)   water,    (3)  gases,  (4)  micro-organisms   and 
vegetable  life.       One  of  the  best  evidences  that  soil  is 
derived  from  rock  is  that  there  are  frequently  found 
in  fields  pieces  of  rock  which  are  actually  rotten,  and, 
when  crushed,  closely  resemble  the  prevailing  soil  of 
the  field.     This  is  particularly  true  of  clay  soils  where 
fragments  of  disintegrated  feldspar  are  found  which, 
when  crushed,  resemble  the  soil  in  which  the  feldspar 


46  SOILS   AND   FERTILIZERS 

was  embedded.  The  process  of  soil  formation  is  a  slow 
one  and  the  various  agents  have  been  at  work  for  an 
almost  unlimited  period. 

49.  Action  of  Heat  and  Cold. — The  cooling  of  the 
earth's  surface,  followed  by  a  contraction  in  volume, 
resulted  in  the  formation  of  fissures  which  exposed   a 
larger  area  to  the  action  of  other  agents.     The  un- 
equal cooling  of  the  rocks  caused  a  partial  separation 
of  the  different  minerals  of  which  the  rocks  were  com- 
posed, resulting  in  the  formation  of  smaller  rock   par- 
ticles  from  the   larger   rock    masses.     This   is    well 
illustrated  by  the  familiar  splitting  and   crumbling  of 
stones  when  heated.  Shaler  estimates  that  a  variation 
of  150°  F.   will  make  a  difference  of   i  inch   in    the 
length  of  a  granite  ledge  100  feet  long.  As  a  result  of 
changes  in   temperature  there  is  a  lessening  of   the 
cohesion  of  the  rock  particles.     The   action   of   frost 
also  is  favorable  to  soil  formation.       The  freezing  of 
water  in  rock  crevices  results  in  breaking  up  the  lock 
masses,  forming  smaller  bodies.     The  force  exerted  by 
water  when  it  freezes  is  sufficient  to  rend  large  rocks. 

50.  Physical  Action  of  Water. — Water  acts  upon 
soils  both  chemically  and  physically.       It  is  the  most 
important  agent  that  has  taken  a  part  in  soil  forma- 
tion.    The  surface  of  rocks  has  been  worn  away  by 
moving  water  and  in  many  cases  deep  ravines  and 
canons  have  been  formed.     This   is   called    erosion. 
The  pulverized  rock,  being  carried  along  by  the  water 
and    deposited    under    favorable    conditions,     forms 
alluvial  soil.     This  physical  action  of  water  is  illus- 


GLACIAL   ACTION  47 

trated  in  the  workings  of  large  rivers  where  the 
pulverized  rock  is  deposited  along  the  river  and  at  its 
mouth.  Large  areas  of  the  soil  in  valleys  and  river 
bottoms  have  been  formed  in  this  way,  and  in  most 
cases  these  soils  are  of  high  fertility.  The  action  of 
water  is  not  alone  confined  to  forming  soils  along 
water  courses,  but  is  equally  prominent  in  the  forma- 
tion of  soils  remote  from  streams  or  lakes,  as  in  the 
case  of  soils  deposited  by  glaciers. 

51.  Glacial  Action. — At  one  time  in  the  earth's 
history,  the  ice-fields  of  polar  regions  covered  much 
larger  areas  than  at  present.20  Changes  of  climate 
caused  a  recession  of  the  ice  fields,  and  resulted  in  the 
movement  of  large  bodies  of  ice,  carrying  along  rocks 
and  frozen  soil.  The  movement  and  pressure  of  the 
ice  pulverized  the  rock  and  produced  soil.  This 
action  is  well  illustrated  at  the  present  time  where 
mountains  rise  above  the  snow  line,  and  the  ice  and 
snow  melting  at  the  base  are  replaced  by  ice  and 
snow  from  farther  up,  moving  down  the  side  of  the 
mountain  and  carrying  along  crushed  stones  and  soil. 
When  the  glacier  receded,  stranded  ice  masses  were 
distributed  over  the  land.  These  melted  slowly  and 
by  their  grinding  action  hollowed  out  places  which 
finally  became  lakes.  The  numerous  lakes  at  the 
source  of  the  Mississippi  River  and  in  central  Min- 
nesota are  supposed  to  have  been  formed  by  glacial 
action.  The  terminal  of  a  glacier  is  called  a  moraine 
and  is  covered  with  large  boulders  which  have  not 
been  disintegrated.  The  course  of  a  glacier  is  fre- 
quently traced  by  the  markings  or  scratches  of  the 


48  SOILS   AND   FERTILIZERS 

mass  on  rock  ledges.  In  glacial  soils,  the  rocks  are 
never  angular,  but  are  smooth  because  of  the  grinding 
action  during  transportation.  The  area  of  glacial  soils 
in  the  northern  portion  of  the  United  States  is  quite 
large.  These  soils  are,  as  a  rule,  fertile  because  of 
the  pulverization  and  mixing  of  a  great  variety  of 
rock. 

52.  Chemical  Action  of  Water. — The  chemical 
action  of  water  has  been  an  important  factor  in  soil 
formation.  While  nearly  all  rocks  are  practically  in- 
soluble in  water  there  is  always  some  material  dis- 
solved, evidenced  by  the  fact  that  all  spring-water 
contains  dissolved  mineral  matter.  When  charged 
with  carbon  dioxide  and  other  gases,  water  acts  as  a 
solvent  upon  rocks.  It  converts  many  oxides,  as  fer- 
rous oxide,  into  hydroxides.  The  chemical  action  of 
water  may  produce  new  compounds  more  soluble  or 
readily  disintegrated,  as  deposits  of  clay,  which  have 
been  formed  from  feldspar  rock  by  the  chemical  and 
physical  action  of  water.  When  rocks  disintegrate, 
chemical  changes  often  occur;  the  addition  of  water 
or  hydration  of  the  molecule,  particularly  of  the  sili- 
cates, is  one  of  the  most  important  chemical  changes. 
Water  takes  as  prominent  a  part  in  the  decay  of  rocks 
as  in  the  decay  of  vegetable  matter.  Limestone  is 
quite  readily  disintegrated  by  water.  Dissolved  min- 
erals produce  many  chemical  changes  in  both  rocks 
and  soils.  The  chemical  action  of  fertilizers  known 
as  fixation  can  take  place  only  in  the  presence  of 
water.  In  fact,  water  is  necessary  for  nearly  all  of  the 


ACTION   OF   VEGETATION  49 

chemical  reactions  in  the  soil  which  result  in  render- 
ing plant  food  available. 

53.  Action  of  Air  and  Gases. — In  the  disintegra- 
tion of  materials  to  form  soil,  air  takes  a  prominent 
but  less  important  part  than  water.     By  the  aid  of 
oxygen,  carbon  dioxide,  and  other  gases  and  vapors 
in  the  air,  rock  disintegration  is  hastened.  The  action 
of  oxygen  changes  the  lower  oxides  to  higher  forms. 
All  rock  contains  more  or  less  oxygen  in   chemical 
combination.     The  carbon  dioxide  of  the  air  under 
some  conditions  favors  the  formation  of  carbonates. 
The  disintegrating  action  of  air,  moisture,  and  frost  is 
illustrated  in  the  case  of  building  stones  which  in 
time    crumble   and   form  a  powder.     This  is  called 
weathering.       Many  of  the  benefits  of  cultivation  are 
due  to  aeration  of  the  soil. 

54.  Action  of  Micro-organisms. — Micro-organisms, 
found  on  the  surface  and  in  the  crevices  of  rocks,  and 
in  decaying  vegetable  matter,  are   active   agents   in 
bringing  about  rock  decay.    The  nitrifying  organisms 
have  taken  an  important  part  in  rendering  soils  fer- 
tile, and  these  with  others  have  aided  in  soil  forma- 
tion.    Some  of  the  organisms  found  on  the  surface  of 
rocks  are  capable  of  producing  carbonaceous  matter 
out  of  the  carbon  dioxide  and  other  compounds  of 
the  air.21     This  action  results   in   adding   vegetable 
matter  to  the  soil. 

55.  Action   of   Vegetation. — Some   of   the   lower 
forms  of  plants  as  lichens   do   not   require   soil    for 
growth,  but  are  capable  of  living  on  the  bare  surface 

(4) 


50  SOILS   AND   FERTILIZERS 

of  rocks,  obtaining  food  from  the  air,  and  leaving  a 
certain  amount  of  vegetable  matter  which  undergoes 
decay  and  is  incorporated  with  the  rock  particles,  pre- 
paring the  way  for  higher  orders  of  plants  which  take 
their  food  from  the  soil.  When  this  vegetable  matter 
decays,  it  enters  into  chemical  combination  with  the 
pulverized  rock,  forming  humates.18  The  disinte- 
grating action  of  plant  roots  and  vegetable  matter 
upon  rocks  has  been  an  important  factor  in  soil  forma- 
tion. The  action  of  vegetable  remains  in  soil  produc- 
tion is  discussed  in  Chapter  III. 

56.  Combined  Action  of  the  Various  Agents. — In 

the  decay  of  rocks  the  various  agents  named — water 
acting  mechanically  and  chemically,  heat  and  cold, 
air,  micro-organisms,  and  vegetation — have  been  act- 
ing jointly,  and  have  produced  more  rapid  disinte- 
gration than  if  each  agent  were  acting  separately. 
Wind  also  has  been  an  important  factor  in  the  pro- 
duction and  modification  of  soils.  The  denuding 
effects  of  heavy  wind  storms  are  well  known.  Large 
areas  of  wind-formed  soils  are  found  in  some  coun- 
tries. .  Sand  dunes  are  transported  by  winds  and  often 
their  subjugation  by  soil-binding  plants  is  necessary 
in  order  to  prevent  their  encroaching  upon  valuable 
farm  lands  and  inundating  villages.  Soils  formed  by 
the  action  of  winds  are  called  aeolian  soils. 
DISTRIBUTION  OF  SOILS 

57.  Sedentary  and  Transported  Soils, — The  place 
which  a  soil  occupies  is   not   necessarily   the   place 
where  it  was  produced ;    that  is.  a  soil  may  be  pro- 


COMPOSITION   OF    ROCK  51 

duced  in  one  locality  and  transported  to  another. 
Soils  are  either  sedentary  or  transported.  Sedentary 
soils  are  those  which  occupy  the  original  position 
where  they  were  formed.  They  usually  have  but 
little  depth  before  rock  surface  is  reached.  The  stones 
in  such  soils,  except  where  modified  by  weathering, 
have  sharp  angles  because  they  have  not  been  ground 
by  transportation.  In  the  southern  part  of  the  United 
States,  east  of  the  Mississippi  River,  there  are  large 
areas  of  sedentary  soils  as  ferrogenous  clays  in  an  ad- 
vanced state  of  decay. 

Transported  soils  are  those  which  have  been  formed 
in  one  locality  and  carried  by  various  agents  as  glaciers, 
rivers  and  winds  to  other  localities,  the  angles  of  stones 
in  these  soils  having  been  ground  off  during  transpor- 
tation. Transported  soils  are  divided  into  classes  ac- 
cording to  the  ways  in  which  they  have  been  formed; 
as,  drift  soils  produced  by  glaciers,  alluvial  soils  formed 
by  rivers  and  deposited  by  lakes,  aeolian  soils  formed 
by  winds,  and  colluvial  soils  formed  of  rocks  and 
debris  from  mountain  sides. 

In  some  localities  volcanic  soils  are  found.  They 
are  extremely  varied  in  texture  and  composition  ; 
some  are  very  fertile  and  contain  liberal  amounts  of 
alkaline  salts  and  phosphates,  while  others  contain  so 
little  plant  food  that  they  are  sterile. 

ROCKS  AND  MINERALS  FROM  WHICH  SOILS  ARE  FORMED 

58,  Composition  of  Rocks. — Rocks  are  composed  of 
either  a  single  mineral  or  of  a  combination  of  minerals. 
Most  of  the  common  minerals  are  definite  chemical 


52  SOILS   AND   FERTILIZERS 

compounds  and  have  a  variable  range  of  composition, 
due  to  the  fact  that  one  element  or  compound  may  be 
partially  or  entirely  replaced  by  another.  Most  rocks 
from  which  soils  have  been  produced  contain  minerals 
as  feldspar,  mica,  hornblende,  and  quartz. 

59.  Quartz  and  Feldspar. — Quartz  is  the  principal 
constituent  of  many  rock  formations.  Pure  quartz  is 
silicic  anhydride  (SiO2).  White  sand  is  nearly  pure 
quartz  or  silica.  Silica  enters  into  combination  with 
many  elements,  forming  a  large  number  of  minerals. 
A  soil  formed  from  pure  quartz  would  be  sterile. 

Feldspar  is  composed  of  silica,  alumina,  and  potash 
or  soda.  Lime  may  also  be  present,  and  replace  a 
part  or  nearly  all  of  the  soda.  If  the  mineral  contains 
soda  as  the  alkaline  constituent  it  is  known  as  albite, 
or  if  mainly  potash  it  is  called  potash  feldspar  or 
orthoclase. 

The  members  of  the  feldspar  group  are  insoluble  in 
acids  and  before  disintegration  takes  place  are  not 
capable  of  supplying  plant  food.  Potash  feldspar 
contains  from  12  to  15  per  cent,  of  potash,  none  of 
which  is  of  value  as  plant  food.  When  feldspar 
undergoes  disintegration  it  produces  kaolin  or  clay. 
A  soil  formed  from  feldspar  is  usually  well-stocked 
with  potash. 

Orthoclase,  AlKSi3O8 Potash  feldspar. 

Albite,          AlNaSi3O8 Sodium  feldspar. 

60.  Hornblende. — The  hornblende  and  augite  groups 
are  formed  by  the  union  of  magnesium,  calcium,  iron, 
and  manganese,  with  silica.  There  are  none  of  the 


ZEOLITES  53 

members  of  the  alkali  family  in  hornblende.  The 
augites  are  double  silicates  of  iron,  manganese,  cal- 
cium, and  magnesium.  Quite  frequently,  phosphoric 
acid  is  present  in  chemical  combination  with  the  iron. 
The  members  of  this  group  are  readily  distinguished 
by  their  color  which  is  black,  brown,  or  brownish 
green.  The  hornblendes  are  insoluble  in  acids,  hence 
unavailable  as  plant  food,  and  when  disintegrated  do 
not  as  a  rule  form  very  fertile  soils. 

61,  Mica, — Mica  is  quite  complex  in  composition, 
is  an  abundant  mineral,  and  is  composed   of   silica, 
iron,  alumina,  manganese,  calcium,  magnesium,  and 
potassium.     Mica  is  a  polysilicate.     The  color  may 
be  white,  brown,  black,  or  bluish  green  owing  either 
to  the  absence  of  iron,   or  to  its  presence  in  various 
amounts.     The   chief   physical    characteristic  of  the 
members  of  this  group  is  the  ease  with  which  they  are 
split  into  thin  layers.     It  is  to  be  observed  that  the 
mica  group  contains  all  of  the  elements  of  both  feld- 
spar and  hornblende. 

Soils  formed  from  disintegrated  mica  are  usually 
fertile,  owing  to  the  variety  of  essential  elements 
present.  Frequently  small  pieces  of  undecomposed 
mica  are  found  in  soils. 

62.  Zeolites. — The  zeolites  are  a  large  group   of 
secondary  or  derivative  minerals  formed  from  disin- 
tegrated   rock.       They    are  polysilicates    containing 
alumina  and  members  of  the  alkali  and  lime  families, 
and  all  contain  water  held   in  chemical   combination. 
They  are  partially  soluble  in  dilute  hydrochloric  acid 


54  SOILS    AND    FERTILIZERS 

and  belong  to  the  group  of  compounds  which  are 
capable,  to  a  certain  extent,  of  becoming  available  as 
plant  food.  In  color,  they  are  white,  gray,  or  red. 
Zeolites  are  quite  abundant  in  clay  and  are  an  import- 
ant factor  in  soil  fertility.  It  is  this  group  of  hydrated 
silicates  which  takes  such  an  important  part  in  the 
process  of  fixation.  The  zeolites,  when  disintegrated, 
particularly  by  glacial  action,  form  very  fertile  soils. 

63.  Granite  is  composed  of  quartz,  feldspar,   and 
mica.    It  is  a  very  hard  rock  and  slow  to  disintegrate. 
The  different  shades  of  granite  depend  upon  the  pro- 
portion in   which  the  various   minerals  are   present. 
Inasmuch  as  granite  contains  so   many  minerals   it 
usually  follows  that  thoroughly  disintegrated  granite 
soil  is  very   fertile.     Pure   powdered   granite  before 
undergoing   disintegration   furnishes  no   plant   food. 
After  weathering,  the  plant  food  gradually   becomes 
available.     Gneiss  belongs   to  the  granite  series  but 
differs  from  true  granite  in  containing  a  larger  amount 
of  mica.      Mica  schist  contains  a  larger  amount   of 
mica  than  gneiss. 

64.  Apatite  or  Phosphate  Rock. — Apatite  is  com- 
posed mainly  of  phosphate  of  lime,  Ca_(PO4)2,  together 
with  small  amounts  of  other  compounds  as  fluorides 
and  chlorides.     This  mineral  is  generally  of  a  green 
or  yellow  color.     It  is  present  in  many  soils  and  is  of 
little  value  as  plant  food  unless  associated  with  or 
ganic  matter  or  some  soluble  salts. 

65.  Kaolin  is  chemically  pure  clay  and  is  formed  by 
the  disintegration  of  feldspar.     When  feldspar  is  de- 


DISINTEGRATION   OF   ROCKS   AND    MINERALS         55 

composed  and  is  acted  upon  by  water  the  potash  is  re- 
moved and  water  of  hydration  is  taken  up,  forming 
the  product  kaolin,  which  is  hydrated  silicate  of  alu- 
mina, Al4(SiO4)3.H2O.  Impure  varieties  of  clay  are 
colored  red  and  yellow  on  account  of  the  presence  of 
iron  and  other  impurities.  Pure  kaolin  is  white,  is 
insoluble  in  acids,  and  is  incapable  of  supplying  any 
nourisment  to  plants.  Clay  soils  are  fertile  on  account 
of  the  other  minerals  and  organic  matter  mixed  with 
the  clay  and  are  usually  well-stocked  with  potash  be- 
cause of  the  incomplete  removal  of  the  potash  from 
the  disintegrated  feldspar.  It  is  to  be  observed  that 
the  term  clay  used-  chemically  means  aluminum  sili- 
cate, while  physically  it  is  any  substance,  the  particles 
of  which  are  less  than  0.005  mm-  in  diameter. 

66.  Disintegration  of  Rocks  and  Minerals. — In  ad- 
dition to  the  rocks  and  minerals  which  have  been 
mentioned,  there  are  many  others  that  contribute  to 
soil  formation  as  limestone  which  is  calcium  carbon- 
ate, dolomite  a  double  carbonate  of  calcium  and  mag- 
nesium, serpentine  a  silicate  of  magnesium,  and  gyp- 
sum or  calcium  sulphate.  All  rocks  and  minerals  are 
subject  to  disintegration  and  change  in  chemical  com- 
position and  physical  properties.  The  process  of  soil 
formation  has  resulted  in  numerous  chemical  and 
physical  changes.  These  changes  are  still  taking  place, 
and  as  a  result  plant  food  is  constantly  being  made 
available. 


56  SOILS   AND   FERTILIZERS 

CHEMICAL  COMPOSITION  OF  ROCKS" 


8 

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es 

c 

g 

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h  1*  Is 

Scd 
rt  be 

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<<  < 

^W          5^          ^0 

SS 

fcto 

^  K 

Quartz.... 

Feldspar  

2O—  2Q 

O—  12       I—  IO      I—  II 

Kaolin.. 

d6 

-7Q 

14 

Apatite 

C7 

^P2O5\ 

s 

V  42  ; 

Mica 

AO—A  ? 

12—77 

5-12 

I—  S 

Hornblende 

O—  IS 

Granite... 

60-80 

IO-IS 

'"' 

2-^ 

67.  Value  of  Geological  Study  of  Soils. — Agri- 
cultural geology  is  a  valuable  aid  in  studying  soil 
problems,  but  like  other  sciences  it  is  incapable  alone 
of  solving  all  of  the  problems  of  soil  fertility. 
Means  have  not  as  yet  been  devised  for  accurately  de- 
termining the  extent  of  rock  disintegration  and  the 
rapidity  with  which  it  has  taken  place  or  the  extent 
to  which  disintegrated  minerals  have  been  removed 
from  rocks  by  leaching  and  other  agencies.  It  is 
known  that  the  rate  of  weathering  of  soils  is  influenced 
by  various  factors,  as  origin,  texture,  composition, 
humidity  and  other  climatic  conditions,  presence  of  de- 
caying organic  matter,  micro-organisms,  mechanical 
treatment  and  manipulation  of  the  soil,  fertilizers, 
sun  light  and  vegetation.  Some  of  these  agencies  for 
soil  disintegration  are  under  the  control  of  the  farmer 
and  are  utilized  by  him  in  rendering  plant  food  avail- 
able. 


CHAPTER  III 


THE  CHEMICAL  COMPOSITION  OF  SOILS 

68.  Elements  Present  in  Soils. — Physically  consid- 
ered, a  soil  is  composed  of  disintegrated  rock  mixed 
with  animal  and  vegetable   matter;    chemically    con- 
sidered, the  rock  particles  are  composed  of  a  large 
number  of  simple  and  complex  compounds,  each  com- 
pound in  turn  being  composed  of  elements  chemically 
united.       Elements  unite  to  form   compounds,   com- 
pounds to  form  minerals,  minerals  to  form  rocks,  and 
disintegrated  rocks   form  soil.     When  rocks  decom- 
pose, the  disintegration,  except  in  a  few  cases,  is  never 
carried  to  the  extent  of  liberating  the  elements,  but 
the  process  ceases  when  the  minerals  have  been  broken 
up  into  compounds.     While  there  are  present  in  the 
crust  of  the  earth  between  65  and   70  elements,  only 
about  15  are  found  in  animal  and  plant  bodies,  and  of 
these  but  12  are  absolutely  essential.       Only  four  of 
the  elements  which  are  of  most  importance  are  at  all 
liable  to  be  deficient  in  soils.     These   four  elements 
are  :  nitrogen,  phosphorus,  potassium,  and  calcium. 

69.  Classification  of  the  Elements. — The  elements 
found  most  abundantly  in  soils  are  divided   into   two 
classes : 


58  SOILS   AND    FERTILIZERS 

Acid-forming  elements  Base-forming  elements 

Oxygen O         Aluminum Al 

Silicon Si         Potassium K 

Phosphorus : P        Sodium Na 

Sulphur S         Calcium Ca 

Chlorine Cl         Magnesium Mg                               «* 

Nitrogen N        Iron Fe                         * 

Hydrogen H 

Carbon C*  j 

Boron,  fluorine,  manganese,  and  barium  are  usually 
present  in  small  amounts,  besides  others  which  may 
be  present  in  traces,  as  the  rare  elements  lithium  and 
titanium. 

For  crop  purposes  the  elements  of  the  soil  may  be 
divided  into  three  classes. 

1.  Essential  elements  most  liable   to  be  deficient:' 
nitrogen,  potassium,  phosphorus,  and  calcium. 

2.  Essential  elements  usually  abundant :  iron,  mag- 
nesium, and  sulphur.  f 

3.  Unnecessary   and    accidental    elements,   usually 
abundant,  as  chlorine,   silicon,   aluminum,  and  man- 
ganese. 

70.  Combination  of  Elements. — In  dealing  with 
the  composition  of  soils,  the  percentage  amounts  of 
the  individual  elements  are  not  given,  except  in  the 
case  of  nitrogen,  but  instead,  the  percentage  amounts 
of  the  various  oxides.  This  is  because  the  elements 
do  not  exist  as  free  elements  in  the  soil,  but  are  com. 
bined  with  oxygen  and  other  elements  to  form  com. 
pounds.  When  considered  as  oxides,  the  acid-  and  base- 
o  rming  elements  may  form  various  compounds  as  : 


SILICON  59 


Calcium  

Silicate 
Phosphate 
Chloride 

w 

Potassium..../,/// 
Sodium  Y/ 

Sulphate 
Carbonate 

Magnesium.y 
Iron  .. 

The  following  reactions  will  explain  some  of  the 
more  elementary  forms  of  combinations  : 

CaO  +  SiO2  =  CaSiO3  CaO   +  N2O5  =  Ca(NO3)2 

3CaO  +  P205=Ca3(P04)2  K2O    +  SO3    =  K2SO, 

CaO  +  S03   =  CaSO,  Na2O  +  SO3    =  Na.SO, 

CaO  +  CO2  =  CaCO3  MgO  +  SO3    =  MgSO4 

When  considered  as  the  oxide,  calcium  may  com- 
bine with  any  of  the  oxides  of  the  acid-forming  ele- 
ments, as  indicated  by  the  reactions,  to  form  salts. 
Each  of  the  compounds  formed  from  the  more  com- 
mon elements  may  have  a  separate  value  as  plant 
food,  hence  it  is  important  to  consider  the  combina- 
tions of  each  element  separately. 

ACID-FORMING  ELEMENTS 

71.  Silicon. — The  element  silicon  makes  up  from 
a  quarter  to  a  third  of  the  solid  crust  of  the  earth  and 
next  to  oxygen  is  the  most  abundant  element  found 
in  the  soil.  Silicon  never  occurs  in  the  soil  in  the 
free  state.  It  either  combines  with  oxygen  to  form 
silica  (SiOa),  or  with  oxygen  and  some  base-forming 
element  or  elements  to  form  silicates.  Silica  and  the 
various  silicates  are  by  far  the  most  abundant  com- 
pounds present  in  the  soil.  Silicon  is  not  one  of  the 
elements  absolutely  necessary  for  plant  growth,  and 


60  SOILS   AND    FERTILIZERS 

even  if  it  were,  all  soils  are  so  abundantly   supplied 
that  it  would  not  be  necessary  to  use   it  in  fertilizers. 

72.  Double  Silicates. — When  two  or  more    base- 
forming  elements  are  united  with  the  silicate  radical, 
a  double  silicate  is  formed.       In  fact  the  double  sili- 
cates are  the  most  common  forms  present  in   soils. 
There  are  also  a  number  of  forms  of  silicic  acid  which 
greatly  increase  the  number  of  silicates,   and   a  study 
of  the  composition  of  soils  is  largely  a  study  of  these 
various  silicates. 

73.  Carbon  is  an  acid-forming  element  and  belongs 
to  the  same  family  as  silicon.    It  is  found  in  the  soil 
as  one  of  the  main  constituents  of  the   volatile   or 
organic  compounds.     Carbon  also  unites  with  oxygen 
and  the  base-forming  elements,  producing  carbonates, 
as  calcium  carbonate  or  limestone.    The  carbon  of  the 
soil  takes  no  direct  part  in  forming  the  carbon  com- 
pounds of  the  plant.      It    is    not    necessary    to  apply 
carbon  fertilizers  to  produce  the  carbon  compounds  of 
plants  because  the  carbon  dioxide  of  the  air  is   the 
source  for  crop  production.     It  is  estimated  that  there 
are  30  tons  of  carbon  dioxide  in  the  air  over  every 
acre  of  the  earth's  surface.22     The  carbon  in  the  soil 
is  an  indirect  element  of  fertility,  because  it  is  usually 
combined  with  elements,  as  nitrogen  and  phosphorus, 
which  are  absolutely  necessary  for  crop  growth. 

74.  Sulphur  occurs  in  all  soils  mainly  in  the  form 
of   sulphates,   as  calcium   sulphate,   magnesium   sul- 
phate and  sodium  sulphate.     It  is  an  important  ele- 
ment of  plant   food.     There   is   generally    less   than 


NITROGEN  6l 

o.io  per  cent,  of  sulphuric  anhydride  in  ordinary 
soils,  but  the  amount  required  by  crops  is  small  and 
there  is  usually  an  abundance  in  all  soils. 

75.  Chlorine  is  present  in  all  soils,  generally   in 
combination  with  sodium,  as  sodium  chloride.  It  may 
be  in  combination  with  other  bases.     Soils  which  con- 
tain more  than  o.io  per  cent,  are,   as  a  rule,  sterile. 
Chlorine  is  present  in  the  soil  in  soluble  forms.     It 
occurs  in  all   plants,   although  it  is   not   absolutely 
necessary  for  plant   growth,  and  its  combination  in 
fertilizers  is  unnecessary.     Chlorine  with  sodium,  as 
common    salt,    is    sometimes    used    as    an     indirect 
fertilizer. 

76.  Phosphorus,  one  of  the  essential  elements  for 
plant  growth,  is  combined  with  both  the  volatile  and 
non-volatile  elements  of  the  soil.    Plants  cannot  make 
use  of  it  in  other  forms  than  those   of  phosphates. 
Phosphorus  is  usually  present  in  the  soil  as  calcium 
phosphate,  magnesium  phosphate,  or  aluminum  phos- 
phate, and  may  also  be  combined   with  the  humus, 
forming  humic  phosphates.     The  form  in  which  the 
phosphates  are  present,  as  available  or  unavailable,  is 
an  important  factor  in  soil  fertility.       Soils  are  quite 
liable  to  be  deficient  in  phosphates,  inasmuch  as  they 
are  so  largely  drawn  upon  by  many  crops,  particularly 
grain  crops  where  the  phosphates  accumulate  in  the 
seed,  and  are  sold  from  the  farm. 

77.  Nitrogen. — This  element  is  present  in  soils  in 
various  forms.     As  a  mineral  constituent  it  is  com- 
bined with  oxygen  and  the  base-forming  elements  as 


62  SOILS   AND   FERTILIZERS 

potassium,  sodium,  or  calcium,  forming  nitrates  and 
nitrites,  which,  on  account  of  their  solubility,  are 
never  found  in  average  soils  in  large  amounts.  Nitro- 
gen is  present  mainly  in  organic  combinations,  being 
associated  with  carbon,  hydrogen,  and  oxygen  as  one 
of  the  elements  forming  the  organic  matter  of  soils. 
Nitrogen  may  also  be  present  in  small  amounts  in  the 
form  of  ammonia,  or  of  ammonium  salts,  derived  from 
rain  water  and  from  the  decay  of  vegetable-  and  ani- 
mal matter.  While  nitrogen  is  present  in  the  air  in 
a  free  state  in  large  amounts,  it  can  be  appropriated 
indirectly  as  food  in  this  form  by  only  a  limited  num- 
ber of  plants.  For  ordinary  agricultural  crops,  par- 
ticularly the  cereals,  nitrogen  must  be  supplied 
through  the  soil  as  combined  nitrogen.  This  element 
is  the  most  expensive  and  is  liable  to  be  the  most  de- 
ficient of  any  of  the  elements  of  plant  food.  No  other 
element  takes  such  an  important  part  in  agriculture  or 
in  life  processes. 

78,  Oxygen. — Oxygen  is  combined  with  both  the 
acid-  and  base-forming  elements  and  is  present  in 
nearly  all  of  the  compounds  of  the  soil.  It  has  been 
estimated  that  about  one-half  of  the  crust  of  the  earth 
is  composed  of  oxygen,  which  is  found  in  large 
amounts  combined  with  silicon,  forming  silica.  That 
which  is  held  in  chemical  combination  in  the  soil 
takes  no  part  in  the  formation  of  plant  tissue.  In  ad- 
dition to  being  present  in  the  soil,  oxygen  constitutes 
eight-ninths  of  the  weight  of  water  and  about  one-fifth 
of  the  weight  of  air.  It  also  forms  about  50  per  cent. 


ALUMINUM  63 

of  the  compounds  found  in  plants  and  animals.  Oxy- 
gen in  the  interstices-  of  the  soil  is  an  active  agent  in 
bringing  about  many  chemical  changes,  as  oxidation 
of  the  organic  matter,  and  disintegration  of  the  soil 
particles. 

79.  Hydrogen. — This  element  is  never  found   in  a 
free  state  in  the  soil,  but  is  combined  with  carbon  and 
oxygen  as  in  animal  and  vegetable  matter,  with  oxy- 
gen to  form  water,  and  in  a  few  cases  with  some  of 
the  base  elements  to  form  hydroxides.  It  is  not  found 
in  large  amounts  in  the  soil,  and  that  which  forms  a 
part  of  the  tissues  of  plants  and  animals  conies  from 
the  hydrogen  in  water.     Hydrogen    in   the   organic 
matter  of  soils  takes  no  part  directly  in  producing  the 
hydrogen  compounds  of  plants.       On    account   of   its 
lightness,  hydrogen  never  makes  up  a  very  large  pro- 
portion, by  weight,  of  the  composition  of  bodies. 

BASE-FORMING  ELEMENTS 

80.  Aluminum  is  present  in  the  soil  in  the  largest 
quantity  of  any  of  the  base  elements.     It  is  calculated 
that  it  forms  from  6  to  10  per  cent,  of  the  solid  crust 
of  the  earth.     As  previously  stated  aluminum  is  one 
of  the  constituents  of  clay,   and  is  not  necessary  for 
plant  growth.       Physically,  however,   the  aluminum 
compounds  take  an  important  part  in   soil    fertility. 
Aluminum  is  usually  in  combination  with  silica  or 
with  silica  and  some  base-forming  element,    as   iron, 
potassium,  or  sodium.     The  various  forms  of  alumi- 
num silicates  are  the  most  numerous  compounds  pres- 
ent in  soils. 


64  SOILS   AND   FERTILIZERS 

81.  Potassium  is  present  in  the  soil  mainly  in  the 
form  of  silicates,  and  is  one  of  the  elements  absolutely 
necessary  for  plant  growth.     The  term  potash  (potas- 
sium oxide,  K2O)  is  usually  employed  when  the  potas- 
sium compounds  are  referred   to.     The  amount  and 
form  of  the  soil  potash  have  an   important   bearing 
upon  fertility.    Potassium  is  one  of  the  three  elements 
of  plant  food  usually  supplied  in  fertilizers.        The 
form    in    which    it   is   present   in    the   soil  and   its 
economic  supply  as  plant  food,  are  important  factors 
of  crop  growth,  and  are  considered  in  detail  in  Chap- 
ter  VIII.     The   amount  of    potash    in  soils   ranges 
from  0.02  to  0.8  per  cent.     In  a  fertile  soil   it  rarely 
falls  below  0.2  per  cent. 

82.  Calcium  is  present  in  the  soil  in  a  variety  of 
forms,   as   calcium    carbonate,    calcium   silicate,    and 
calcium    phosphate.       The    calcium   oxide  (CaO)  of 
the  soil  is  generally  spoken  of  as  the  lime   content. 
Calcium  carbonate  and  sulphate  are  important  factors 
in  imparting  fertility.       A  subsoil  with  a  good  supply 
of  lime  will  stand  heavy  cropping  and  remain  in  ex. 
cellent   chemical    and    physical    condition    for    crop 
growth.     In  a  good  soil  there  is  usually  0.2   per  cent, 
or  more  of  lime  mainly  as  calcium  carbonate. 

83.  Magnesium  is  present  in  all  soils  and  is  usually 
associated  with  calcium,  forming  the  mineral    dolo- 
mite, which    is   a  double  carbonate   of   calcium    and 
magnesium.     Magnesium  may  also  be  present  in   the 
soil  in  the  form  of  magnesium  sulphate  or  magnesium 
chloride.     All  crops  require  a  certain  amount  of  mag- 


ACID-SOLUBLE   MATTER   OP   SOILS  65 

nesia  in  some  form,  in  order  to  reach  maturity  and 
produce  fertile  seeds.  There  is  generally  in  all  soils 
an  amount  sufficient  for  crop  purposes,  hence  it  is  not 
necessary  to  consider  this  element  in  connection  with 
fertilizers. 

84.  Sodium  is  found  in  the  soil  mainly  as  sodium 
silicate,  and  is  present  to  about  the  same  extent  as 
potassium  which   it   resembles   chemically   in  many 
ways.     It  cannot,  however,  replace   in  plant  growth 
the  element  potassium.      Inasmuch  as  sodium  takes 
an  indifferent  part  in  plant  nutrition  it  is  never  used 
as  a  fertilizer  except  in  an  indirect  way. 

85.  Iron  is  an  element  necessary  for  plant  food  and 
is  found  in  all  soils  to  the  extent  of  from   i   to  4  per 
cent.     Crops  require  only  a  small   amount  of  iron, 
hence   there  is  always  sufficient  for  crop  purposes. 
Iron  is  present  in  soils  in  the  form  of  oxides,  hydrox- 
ides, and  silicates. 

FORMS  OF  PLANT  FOOD 

86.  Three   Classes   of   Compounds. — For    agricul- 
tural purposes,  the  compounds  present  in  soils  may  be 
divided  into  three  classes  :17    (i)    Compounds  soluble 
in  water  and  dilute   organic  and  mineral  acids ;    (3) 
compounds  soluble  in  more  concentrated  acids ;  (3)  in- 
soluble compounds  decomposed  by  strongest  acids  and 
fluxes. 

87.  Water-  and  Dilute  Acid-soluble  Matter  of  Soils. 

— This  class  includes  silicates  and  other  compounds  of 
potash,  soda,  lime,  magnesia,  phosphorus,  etc.,  which 
are  soluble  in  the  soil  water  and  in  very  dilute  organic 

(5) 


66  SOILS   ANE>   FERTILIZERS 

and  mineral  acids,  and  represents  the  most  soluble  and 
the  most  active  and  valuable  forms  of  plant  food. 
There  is  only  a  very  small  amount  in  these  forms. 
In  100  pounds  of  soil,  rarely  more  than  0.005  pound 
of  any  one  of  the  important  elements  is  soluble  in 
the  soil-water  or  more  than  0.05  pound  in  dilute  or- 
ganic acids. 

Experiments  have  shown  that  the  soluble  plant 
food  from  a  fertile  soil  is  not  sufficient  for  plant 
growth.85  When  oats,  wheat  and  barley  were  seeded 
in  prepared  sand  and  watered  with  the  leach- 
ings  from  a  pot  of  fertile  soil,  they  made  only  a  lim- 
ited growth.  For  comparisons  with  plants  grown  in 
fertile  soil,  see  Plate  I.  The  oats  grown  in  the  pre- 
pared sand  and  watered  with  soil  leachings  assimilated 
only  25  per  cent,  as  much  phosphoric  acid  as  the 
plants  grown  in  fertile  soil. 

88.  Acid  Soluble  Matter  of  Soils,— The  plant  food 
of  the  second  class  is  in  a  somewhat  more  insoluble 
form,  and  consists  of  all  those  compounds  and  zeolitic 
silicates  which  are  soluble  in  hydrochloric  acid  of 
23  per  cent,  strength,  sp.  gr.  1.115.  This  represents 
the  limit  of  the  solvent  action  of  the  roots  of  plants.17 
In  this  second  class  are  also  included  all  of  the  mineral 
elements  combined  with  the  humus  and  soluble  in 
dilute  alkalies.  As  a  rule,  not  over  15  or  20  per  cent, 
of  the  total  soil  is  in  forms  soluble  in  hydrochloric 
acid,  and  of  the  more  important  elements  only  i  to  6 
per  cent,  form  a  part  of  this  15.  In  200  samples  of  soil, 
the  potash,  nitrogen,  lime,  magnesia,  and  phosphoric 
and  sulphuric  acids,  amounted  to  3.5  per  cent.  In 


PI.ATK  I, 


ACID-INSOLUBLE   MATTER   OF   SOILS 

/  2.3. 


Total  /nsolub/e  Matter- 


Fig.  17.     Graphic  composition  of  200  soils, 
i.  Nitrogen.     2.  Potash.     3.  Phosphoric  acid. 

many  fertile  soils  the  sum  of  the  nitrogen,  phosphoric 
acid,  potash,  lime,  magnesia,  and  sulphuric  and  car- 
bonic anhydrides  is  less  than  1.50  per  cent.  This 
means  that  in  every  100  pounds  of  soil  there  are  only 
from  1.5  to  3.5  pounds  of  matter  which  can  take  any 
active  part  in  the  support  of  a  crop,  and  96  to  98.5 
pounds  are  present  simply  as  so  much  inert  material. 
Not  all  of  the  plant  food  soluble  in  hydrochloric  acid 
is  equally  valuable.  In  fact,  the  acid  represents  more 
than  the  limit  of  the  crop's  feeding  power,  when  there 
is  not  enough  of  more  soluble  forms  to  aid  in  the  first 
stages  of  growth. 

89.  Acid-Insoluble  Matter  of  Soils. — This  class  in- 
cludes all  of  those  compounds  of  the  soil  which  re- 
quire the  joint  action  of  the  highest  heat  and  the 
strongest  chemicals  in  order  to  decompose  them.  The 


68 


SOILS   AND   FERTILIZERS 


insoluble  residue  obtained  after  digesting  a  soil  with 

strong  hydrochloric  acid,  contains  potash,  soda,  and 

limited  amounts  of  magnesia, 

and   phosphoric   acid,    with 

other  elements  which  are  of 

no     value     as    plant    food. 

When  seed  was  planted  in 

soil    extracted   with   strong 

hydrochloric  acid,   it   made 

no  growth  after  the  reserve 

food  in    the  seed  had  been 

exhausted.      A  plant  grown 

in  such  a  soil  is  shown   in 

the     illustration,1?  Fig.   18. 

The  acid-insoluble  matter 
of  soils  is  capable  of  under- 
going disintegration  and  in 
time  may  be  changed  to  the 
second  or  zeolitic  class  of 
silicates.  This  process,  how- 
ever, is  too  slow  to  be  relied 
upon  as  an  immediate  source 
of  plant  food. 

In  the  following  table  the 
percentage  amounts  of  com-  FiS-  l8-  Oat  Plant  Srown  in 

soil  extracted  with  hydro- 
pounds  soluble  and  insoluble  chloric  acid. 

in  hydrochloric  acid  are  given  :17 


SOLUBLE  AND  INSOLUBLE  POTASH,  ETC.      69 

Wheat  Heavy  clay             Grass  and 
soil.  soil.                   grain  soil. 
Solu-    Insolu-  Solu-     Insolu-  Solu-     Insolu- 
ble in      ble  ble  in       ble  ble  in        ble 
HC1    residue  HC1     residue  HC1      residue 

Insoluble  matter...  63.07  84.77  84.08     

Potash 0.54  2.18  0.21  3.46  0.30  1.45 

Soda 0.45  3.55  0.22  2.95  0.25  0.25 

Lime 2.44  0.36  0.48  0.16  0.51  0.35 

Magnesia 1.85  0.25  0.34  0.47  0.26  0.46 

Iron 4.18  0.78  3.76  0.72  2.56  1.07 

Alumina 7.89  5.54  6.26  5.44  2.99  9.72 

Phosphoric  acid....  0.38  0.12  0.08  0.23  0.05 

Sulphuric  acid o.n  0.24  0.09  0.25  0.08  0.02 

The  insoluble  matter,  after  digestion  with  hydro- 
chloric acid,  was  submitted  to  fusion  analysis,  and  the 
figures  given  under  insoluble  residue  represent  the 
amounts  of  potash,  soda,  etc.,  insoluble  in  acids.  In 
the  clay  soil,  94  per  cent,  of  the  total  potash  is  in 
forms  insoluble  in  hydrochloric  acid. 

90.  Soluble  and  Insoluble  Potash  and  Phosphoric 
Acid. — From  the  preceding  table  it  is  to  be  observed 
that  the  larger  portion  of  the  potash  in  the  soil  is  in- 
soluble in  hydrochloric  acid.  A  soil  may  contain 
from  2  to  3  per  cent,  of  total  potash,  and  90  per  cent, 
or  more  may  be  in  such  firm  chemical  combination 
with  aluminum,  silicon,  and  other  elements,  as  to  re- 
sist the  solvent  action  of  plant  roots.  The  larger  por- 
tion of  the  phosphoric  acid  of  the  soil  is  soluble  in 
hydrochloric  acid.  In  some  soils,  however,  from  20 
to  40  per  cent,  is  present  as  the  third  class  of  com- 
pounds. When  a  soil  is  digested  with  hydrochloric 
acid,  the  insoluble  residue  is  usually  a  fine,  gray 
powder.  Some  clay  soils  retain  their  red  color  even 
after  treatment  with  acids  showing  that  the  iron  is  in 


70  SOIIvS   AND    FERTILIZERS 

part  in  chemical  combination  with  the  more  complex 
silicates. 

In  order  to  decompose  the  insoluble  residue  obtained 
from  the  treatment  with  hydrochloric  acid,  fluxes,  as 
sodium  carbonate  and  calcium  carbonate,  are  employed 
which  act  upon  the  complex  silicates  at  a  high  tem- 
perature, and  produce  silicates  soluble  in  acids.  Plants, 
however,  are  unable  to  obtain  food  in  such  complex 
forms  of  chemical  combination. 

91.  Action  of  Organic  Acids  upon  Soils. — Dilute 
organic  acids,  as  a  i  per  cent,  solution  of  citric  acid, 
have  been  proposed  as  solvents  for  the  determination 
of  easily  available  plant  food.  It  has  been  shown  in 
the  case  of  the  Rothamsted  soils  which  have  produced 
50  crops  of  grain  without  manures,  and  which  are 
markedly  deficient  in  available  phosphoric  acid,  that 
a  i  per  cent,  solution  of  citric  acid  dissolved  only  0.003 
per  cent,  of  phosphoric  acid  while  the  soil  contained  a 
total  of  o.i  2  per  cent.  In  the  case  of  an  adjoining 
plot  which  had  received  phosphate  manures  until  the 
soil  contained  a  sufficient  amount  of  available  phos- 
phoric acid  to  produce  good  crops,  there  was  present 
0.03  per  cent,  of  phosphoric  acid  soluble  in  a  i  per 
cent,  citric  acid  solution.23 

Dilute  organic  acids  are,  to  a  certain  extent,  capable 
of  showing  deficiency  of  plant  food.  A  soil  which 
shows  0.03  per  cent,  of  potash  or  phosphoric  acid  sol- 
uble in  i  per  cent,  citric  acid  is,  as  a  rule,  well  stocked 
with  available  phosphoric  acid.  Prairie  soils  of  high 
fertility  yield  from  0.03  to  0.05  per  cent,  of  both  pot- 


ACTION   OF   ORGANIC   ACIDS   UPON  SOILS  7 1 

ash  and  phosphoric  acid  soluble  in  dilute  organic 
acids  ;  soils  which  are  deficient  in  these  elements  usu- 
ally contain  less  than  o.oi  per  cent. 

The  action  of  a  single  organic  acid  of  specific 
strength  cannot  be  taken  as  the  measure  of  fertility 
for  all  soils  and  crops  alike,  because  different  plants 
do  not  have  the  same  amount  or  kind  of  organic  acid 
in  the  sap.  Of  the  various  organic  acids,  citric  pos- 
sesses the  greatest  solvent  action  upon  lime,  magnesia, 
and  phosphoric  acid,  while  oxalic  has  the  strong- 
est solvent  action  upon  the  silicates.  Tartaric  acid 
appears  to  be  less  active  as  a  solvent  than  either  citric 
or  oxalic  acid.  The  combined  use  of  dilute  organic 
acids,  as  citric,  with  hydrochloric  acid  (sp.  gr.  1.115), 
will  generally  give  an  accurate  idea  of  the  character 
of  a  soil. .  A  fifth-normal  solution  of  hydrochloric  acid 
has  also  been  proposed  as  a  measure  of  the  soil's  active 
phosphoric  acid,  and  has  given  satisfactory  results.24 

The  use  of  dilute  organic  acids  renders  it  possible 
to  detect  small  amounts  of  readily  soluble  phosphoric 
acid  and  potash.  It  has  been  stated  that  when  a  soil 
has  been  manured  a  few  years  with  a  phosphate  fer- 
tilizer and  brought  into  good  condition  as  to  avail- 
able phosphoric  acid,  a  chemical  analysis  will  fail  to 
detect  any  difference  in  the  soil  before  or  after  the 
treatment  with  fertilizer.  In  the  case  of  hydrochloric 
acid  as  a  solvent,  this  is  true  because  an  acre  of  soil 
to  the  depth  of  one  foot  weighs  about  3,500,000  Ibs. 
and  500  pounds  of  phosphoric  acid  would  increase  the 
total  amount  of  phosphoric  acid  about  0.015  per  cent. 
When  a  dilute  organic  acid  is  used,  only  the  more 


SOILS   AND   FERTILIZERS 


easily  soluble  phosphoric  acid  is  dissolved,  and  this 
readily  allows  fertilized  and  unfertilized  soils  to  be 
distinguished.  By  the  use  of  dilute  organic  acids  and 
salts  decided  differences  have  been  shown  between  soils 
fertilized  and  unfertilized  with  potash.26 

92.  Sampling  of  Soils. — A  composite  sample  of 
soil  is  obtained  from  a  field  by  taking  several  small 
samples  to  a  depth  of  6  to  9  inches,  from  different 
places,  and  uniting  them  to  form  one  sample.  Samples 
of  subsoil  also  are  taken  from  the  same  places.  There 
is  usually  a  sharp  line  of  demarkation  between  the 
surface  and  subsoils.  It  is  the  aim  to  secure  in  both 
cases  as  representative  samples  as  possible.  All 
coarse  stones  and  roots  are  removed  and  a  record  is 
made  of  the  amount  of  these  materials.  The  soil  is 
air-dried,  the  hard  lumps  are  crushed,  and  the  mate- 
rials mixed  and  passed  through  a  sieve 
with  holes  0.5  mm.  in  diameter.  Only 
the  fine  earth  is  used  for  the  chemical 
analysis. 

93.  Analysis    of  Acid- soluble   Ex- 
tract of  Soils. — Ten  grams  of  soil  are 
weighed  into  a   soil   digestion    flask, 
and    10  cc.   hydrochloric  acid  (sp.  gr. 
1.115),  are  added  for  every  gram  of  soil 
used.     The  soil  digestion  flask  is  then 
placed   in  a  hot    water-bath    and   the 
digestion    carried  on  for  twelve  hours 
Fig.  19.    Diges-    at  the  temperature  of  boiling  water.27 
tion  flask.        After  digestion  is  completed  the  con- 
tents of  the  flask  are  transferred  to  a  filter  and  separated 


ACID-SOLUBLE   EXTRACT   OF  SOILS 


73 


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74  SOILS   AND   FERTILIZERS 

into  an  insoluble  part,  and  the  acid  solution  which 
contains  the  soluble  compounds  of  the  various  elements. 
The  table  on  page  73  gives  a  general  idea  of  the 
process  of  soil  analysis.  One-half  of  the  acid  solu- 
tion is  used  for  obtaining  the  metals  as  noted 
on  page  73.  The  second  half  is  divided  into  two 
portions.  The  first  portion  is  used  for  the  deter- 
mination of  phosphoric  acid,  which  is  precipitated 
with  ammonium  molybdate.  The  second  portion  is 
used  for  the  determination  of  sulphuric  acid,  which  is 
precipitated  as  barium  sulphate.  Carbon  dioxide 
is  determined  in  a  fresh  portion  of  the  original  soil  j 
the  acid  is  liberated  with  hydrochloric  acid  and  the 
carbon  dioxide  retained  by  absorbents  and  weighed. 
The  nitrogen  and  humus  are  determined  in  separate 
portions  of  the  original  soil.  The  analysis  of  soils 
involves  the  use  of  accurate  and  well-known  methods 
of  analytical  chemistry,  a  discussion  of  which  would 
not  be  germane  to  this  work. 

94.  Value  of  Soil  Analysis. — Opinions  differ  as  to 
the  value  of  soil  analysis.  It  is  claimed  by  some  that 
a  chemical  analysis  of  a  soil  is  of  no  practical  value 
because  it  fails  to  give  the  amount  of  available  plant 
food.  A  soil  may  have,  for  example,  0.4  per  cent,  of 
potash  soluble  in  hydrochloric  acid  and  still  not  con- 
tain sufficient  available  potash  to  produce  a  good  crop, 
while  another  soil  may  contain  0.2  per  cent,  of  potash 
soluble  in  hydrochloric  acid  and  produce  good  crops. 
While  these  facts  are  frequently  true,  it  does  not 
necessarily  follow  that  the  chemical  analysis  of  a  soil 


VALUE   OF   SILT   ANALYSIS  75 

is  of  no  value.  Other  solvents  than  hydrochloric  acid 
are  used  in  soil  analysis  with  excellent  results.  Hydro- 
chloric acid  is  generally  used  because  it  represents  the 
limit  of  fhe  solvent  power  of  plants.17.  The  figures 
obtained  by  the  use  of  hydrochloric  acid  are  valuable 
inasmuch  as  they  indicate  whenever  an  element  is 
present  in  amounts  which  are  too  limited  to  admit  of 
crop  production.  Suppose  a  soil  contain  0.02  per  cent, 
of  acid-soluble  potash;  this  would  be  too  small  an 
amount  to  produce  good  crops.  On  the  other  hand, 
the  soil  might  contain  0.5  per  cent,  and  yet  not  have 
sufficient  available  potash  for  crop  growth.  Hence 
it  is,  that  in  interpreting  results,  the  hydrochloric  acid 
solvent  may  show  when  a  soil  is  wholly  deficient  in 
any  one  element,  as  is  sometimes  the  case,  but  it  does 
not  necessarily  show  a  deficiency  in  the  case  of  a  soil 
rich  in  acid-soluble  potash ;  this  can,  however,  be  ap- 
proximately indicated,  by  the  use  of  other  solvents,  as 
explained  in  Section  91.  Hydrochloric  acid  is  mainly 
valuable  in  determining  the  general  character  of  the 
soil,  rather  than  its  amount  of  available  plant  food. 

In  the  analysis  of  soils  their  reaction  as  acid,  alka- 
line, or  neutral,  should  be  determined,  because  plant 
food  exists  in  a  different  form  in  each  class  of  soils. 
If  a  soil  contain  from  0.3  to  0.5  per  cent,  or  more  of 
lime  and  from  o.i  to  0.4  per  cent,  of  combined  carbon 
dioxide,  and  is  not  strongly  alkaline,  there  is  a  reason- 
able content  of  lime  carbonate.  If,  however,  the  soil 
contain  only  a  trace  of  carbon  dioxide,  the  lime  is 
not  present  as  carbonate,  but  is  probably  present  as  a 


76  SOILS   AND   FERTILIZERS 

silicate,  in  which  case  the  soil  may  be  deficient  in  ac- 
tive lime  compounds. 

In  the  case  of  phosphoric  acid,  a  soil  which  gives 
an  alkaline  or  neutral  reaction,  contains  0.15  per 
cent,  of  phosphorus  pentoxide  and  is  well  supplied  with 
organic  matter  and  lime,  is  amply  provided  with  phos- 
phoric acid,  and  under  such  conditions  the  extensive 
use  of  phosphate  fertilizers  is  not  required,  except  pos- 
sibly for  special  crops.  Hilgard  states  that  should 
the  per  cent,  of  phosphoric  acid  be  as  low  as  0.05, 
there  is,  in  all  probability,  a  poverty  of  this  element. 
It  frequently  happens  that  in  acid  soils  the  phosphoric 
acid  is  unavailable  until  a  lime  fertilizer  is  used  to 
neutralize  the  acid. 

Soils  containing  less  than  0.07  per  cent,  of  total 
nitrogen  are  usually  deficient.  A  soil  containing  as 
high  as  0.15  or  0.2  per  cent,  of  nitrogen  may  fail  to  re- 
spond to  crop  production.  Such  cases  are  generally 
due  to  some  abnormal  condition  of  the  soil,  as  a  lack 
of  alkaline  compounds  which  are  necessary  for  nitri- 
fication. The  appearance  of  the  crop  is  the  best  indi- 
cation as  to  a  deficiency  of  nitrogen. 

A  soil  which  contains  less  than  o.io  percent,  of  pot- 
ash soluble  in  hydrochloric  acid  is  quite  apt  to  be  de- 
ficient in  this  element.  Soils  which  contain  0.5  per 
cent,  or  more  of  lime  carbonate  will  produce  good 
crops  on  a  smaller  working  supply  of  potash  than  soils 
which  are  proverty-stricken  in  lime.  As  a  rule  the 
best  agricultural  soils  contain  from  0.3  to  0.6  per  cent, 
of  potash.  Sandy  soils  of  good  depth  may  contain 


VALUE   OF   SILT   ANALYSIS  77 

less  plant  food  than  the  figures  given,  and  not  be  in 
need  of  fertilizers. 

The  term  volatile  matter  is  sometimes  confused  with 
the  term  organic  matter.  The  volatile  matter  includes 
the  organic  matter  and  the  water  which  is  held  in 
chemical  combination  as  in  the  hydrated  silicates.  A 
soil  may  have  a  high  per  cent,  of  volatile  matter  and 
contain  very  little  organic  matter.  Indeed  all  clays 
contain  from  5  to  9  per  cent,  of  water  of  hydration. 
The  per  cent,  of  humus,  as  will  be  explained  in  the 
next  chapter,  does  not  represent  all  of  the  organic 
matter. 

The  best  results  are  obtained  from  soil  analyses 
when  an  extended  study  is  made  of  the  soils  of  a  lo- 
cality. Then  an  unknown  soil  of  that  locality  can  be 
compared  with  a  productive  soil  of  known  composition. 
An  isolated  soil  analysis,  like  an  isolated  analysis  of 
well  water,  frequently  fails  in  its  object  because  of  a 
lack  of  proper  normal  standards  for  comparison. 
When  extended  series  of  soil  analyses  have  been 
made,  much  valuable  information  has  been  obtained. 

Suppose  a  soil  contain  0.40  per  cent,  of  acid-soluble 
potash  and  field  experiments  indicate  that  there  is  a 
deficiency  of  available  potash.  This  may  be  due  to 
some  abnormal  condition  of  the  soil,  as  an  insufficient 
amount  of  other  alkaline  compounds  as  calcium  car- 
bonate to  take  the  place  of  the  potash  which  has  been 
withdrawn  by  the  crop,  in  which  case  the  deficiency 
of  potash  can  be  remedied  without  purchasing  solu- 
ble potash  fertilizer,  to  become  insoluble  by  fixation 
processes.  If  a  soil  contain  only  0.04  per  cent,  of 


y8  SOILS   AND    FERTILIZERS 

acid-soluble  potash,  the  purchasing  of  potash  fer- 
tilizers is  more  necessary,  but  with  0.40  per  cent. 
of  acid-soluble  potash  the  way  is  open  to  render  this 
potash  available  for  crops.  The  various  ways  of  ren- 
dering acid-insoluble  potash  and  other  compounds 
available  for  crop  production,  as  by  rotation  of  crops, 
use  of  farm  manures,  use  of  lime  and  green  manures, 
or  by  different  methods  of  cultivation  have  not  been 
sufficiently  studied  as  yet  to  offer  a  solution  to  all  of 
the  problems  of  how  to  render  inert  plant  food  avail- 
able. 

95.  Distribution  of  Plant  Food. — In  studying  the 
chemical  composition  of  a  soil,  the  surface  soil  and 
the  subsoil  both  require  consideration.  It  frequently 
happens  that  the  surface  soil  and  subsoil  have  entirely 
different  chemical,  as  well  as  physical,  properties,  and 
that  a  soil  fault,  as  lack  of  potash  in  the  surface  soil,  is 
corrected  by  a  high  per  cent,  of  that  element  in  the 
subsoil.  This  is  particularly  true  of  the  western  prairie 
soils,  where  the  surface  soils  generally  contain  less 
potash  and  lime,  but  more  nitrogen  and  phosphoric 
acid  than  the  subsoils.  When  jointly  considered  the 
surface  and  subsoil  have  strong  crop-producing  powers, 
but  if  considered  separately  each  would  have  weak 
points. 

Since  crops  take  their  food  mainly  from  the  silt  and 
clay,  the  amount  of  plant  food  present  in  these  grades 
of  particles  determines  largely  the  reserve  fertility  of 
the  soil.  A  soil  in  which  70  per  cent,  of  the  total 
potash  is  present  in  the  silt  and  clay,  is  in  better  con- 
dition for  crop  production  than  a  similar  soil  with  a 


COMPOSITION    OF   TYPICAL   SOILS  79 

like  amount  of  potash  which  is  present  mainly  in  the 
sand.  Because  a  soil  has  a  given  composition,  it  does 
not  follow  that  all  of  the  different  grades  of  particles 
have  the  same  composition.  In  fact  the  different 
grades  of  soil  particles  in  one  soil  may  have  as  varied 
a  composition  as  is  met  with  among  different  soils.26 

The  figures  under  i  in  the  table  give  the  composi- 
tion of  the  particles,  while  under  2  are  given  the  re- 
sults calculated  on  the  basis  of  the  total  amount  of 
each  element.  For  example,  the  clay  contains  1.47 
per  cent,  of  potash,  while  50.8  per  cent,  of  the  total 
potash  of  the  soil  is  in  the  clay  particles. 

A  soil  may  contain  a  comparatively  low  per  cent,  of 
potash  or  phosphoric  acid,  mainly  in  the  finer  particles 
and  evenly  distributed  so  that  the  crop  is  better  sup- 
plied with  food  than  if  more  were  present  in  the 
larger  particles,  unevenly  distributed.  The  distribu- 
tion of  the  plant  food  in  the  soil  has  not  been  so  ex- 
tensively studied  as  the  question  of  total  plant  food. 
The  distribution  of  plant  food  in  both  surface  soil  and 
subsoil,  as  well  as  in  the  various  grades  of  soil  parti- 
cles, is  an  important  factor  of  fertility. 

96.  Composition  of  Typical  Soils.— A  few  exam- 
ples are  given,  in  tabular  form,  of  the  chemical  com- 
position of  soils  from  different  regions  in  the  United 
States.  On  account  of  variations  in  the  same  locality, 
the  figures  represent  the  composition  of  only  limited 
areas  of  soils.  There  have  been  made  in  the  United 
States  a  large  number  of  soil  analyses,  which  as  yet 
have  not  been  compiled  nor  studied  in  a  systematic 
way. 


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SOILS   AND   FERTILIZERS 


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82 


SOILS   AND   FERTILIZERS 


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IMPROVING   ALKALI   SOILS  83 

97.  Alkaline  Soils. — When  a  soil  contains  enough 
alkaline  salts  as  sodium   sulphate,  sodium  or  potas- 
sium carbonate  or  chloride,  to  be  destructive  to  vege- 
tation, it  is  called  an  '  alkali '  soil.     These  soils   are 
found   in  semi-arid  regions,  and  wherever  conditions 
have  been  such  that  the  alkaline  compounds  have  not 
been    drained    from    the    soil.     Occasionally   calcium 
chloride  is  the  destructive  material.     Chlorine  in  any 
ordinary    combination    is    destructive    to    vegetation 
when  present  to  the  extent  of  more   than   T   part  per 
1000  parts  of    soil.     Of   the   various   alkaline    com- 
pounds  potassium   carbonate  is  one  of  the  most  in- 
jurious.    Sodium  sulphate  is  a  milder  form  of  alkali. 
When  evaporation  takes  place,  the  alkaline  compounds 
are  deposited  as  a  coating  on  the  surface  of  the  soil. 
Many  soils  supposed  to  be  strongly  alkaline,  because 
a  white  coating  is  formed  on  the  surface,  simply  con- 
tain so  much  lime  carbonate  that  a  deposit  is  formed. 
Excellent  soils  have  been  passed  over  as  (  alkali '  soils 
when  in  reality  they  are  limestone  soils. 

98.  Improving  Alkali  Soils,27 — When  a  large  tract 
of  alkali  is  to  be  brought  under  cultivation  the  amount 
and  kind  of  prevailing  alkaline  compound  should  be  de- 
termined by  chemical  analysis.    It  frequently  happens 
that  drainage  followed  by  deep  and  thorough-  cultiva. 
tion  is  all  the  treatment  necessary.     If  the  prevailing 
alkali  is  sodium  carbonate  a  dressing  of  land  plaster 
may  be  applied  so  as  to  change  the  alkali  from  sodium 
carbonate  to  sodium  sulphate,  a  less  destructive  form, 
the  reaction  being 

Na2C03  +  CaS04  =  CaCO3  +  N 


84  SOILS   AND    FERTILIZERS 

Some  shrubs,  as  grease  wood,  and  weeds,  as  Russian 
thistle,  take  from  the  soil  large  amounts  of  alkaline 
matter,  and  it  is  sometimes  advisable  to  remove  a 
number  of  such  crops  so  as  to  reduce  the  alkali.  A 
slightly  beneficial  effect  is  sometimes  noticed  on  small 
<  alkali '  spots  where  straw  is  burned  and  the  ashes  are 
used,  forming  potassium  silicate.  As  a  rule  ashes  are 
more  injurious  than  beneficial,  on  an  'alkali'  soil. 
Irrigation  and  thorough  drainage,  if  continued  long 
enough,  will  effect  a  permanent  cure.  Irrigation 
without  drainage  may  cause  a  more  alkaline  condition 
by  bringing  to  the  surface  subsoil  alkali.  The  waters 
from  some  streams  and  weils  are  unsuited  for  irriga- 
tion on  account  of  containing  too  much  alkaline  mat- 
ter. Mildly  alkaline  soils  will  usually  repay  in  crop 
production  all  the  labor  which  is  expended  in  making 
them  productive,  and  when  brought  under  cultivation 
are  frequently  very  fertile  soils.  A  small  amount  of 
alkaline  compounds  in  a  soil  is  beneficial ;  in  fact, 
many  soils  would  be  more  productive  if  they  contained 
more  alkaline  matter. 

99.  Improving  Small  Tracts  of  < Alkali'  Land.— 
When  the  places  are  located  so  that  they  can  be  under- 
drained  at  comparatively  little  expense,  this  should  be 
done,  as  it  will  prove  the  best  and  most  permanent 
way  of  removing  the  alkali.  Good  surface  drainage 
should  also  be  provided.  Quite  frequently  a  quarter 
or  more  of  the  total  alkali  in  the  soil  will,  in  a  dry 
time,  be  found  near  and  on  the  surface.  In  such  cases, 
and  if  the  spots  are  small,  a  large  amount  of  alkali 
can  be  removed  by  scraping  the  surface  and  then  cart- 


ACID   SOILS  85 

ing  the  scrapings  away  and  dumping  them  where  they 
can  do  no  damage. 

When  preparing  an  *  alkali  '  spot  for  a  crop,  deep 
plowing  should  be  practiced,  so  as  to  open  up  the  soil 
and  remove  the  excess  of  alkaline  matter  from  the 
surface.  Where  manure,  particularly  horse  manure, 
can  be  obtained  these  spots  should  be  manured  very 
heavily.  The  horse  manure,  when  it  decomposes,  fur- 
nishes acid  products,  which  combine  with  the  alkaline 
salts.  The  manure  also  prevents  rapid  surface  evapora- 
tion. Oats  are  about  the  safest  grain  crop  to  seed  on 
an  <  alkali '  spot  because  the  oat  plant  is  capable  of 
thriving  in  an  alkaline  soil  where  many  other  grain 
crops  fail. 

'Alkali'  soils  are  usually  deficient  in  available 
nitrogen.  The  organism  which  carries  on  the  work 
of  changing  the  humus  nitrogen  to  available  forms 
cannot  thrive  in  a  strong  alkaline  solution.  In  many 
of  these  soils,  as  demonstrated  in  the  laboratory,  nitri- 
fication cannot  take  place.  After  thorough  drainage  and 
preparation  for  a  crop,  a  few  loads  of  good  soil  from  a 
fertile  field  sprinkled  on  '  alkali '  spots  will  do  much  to 
encourage  nitrification,  by  introducing  the  nitrifying 
organisms. 

100.  Acid  Soils. — When  a  soil  is  deficient  in  active 
alkaline  matter,  humic  acids  are  formed  from  the 
decay  of  animal  and  vegetable  substances.  Acid  soils 
are  readily  detected  by  the  reaction  which  they  give 
with  sensitive  litmus  paper.  In  making  the  test  the 
moistened  soil  is  pressed  against  the  blue  litmus 
paper  which  changes  to  red  in  the  presence  of  free 


86  SOILS   AND   FERTILIZERS 

acids.  Acid  soils  are  made  productive  by  using  lime 
and  other  alkaline  matter  to  neutralize  the  humic 
acid  before  applying  farm  and  other  manures.  Acid 
soils  are  not  suitable  for  the  production  of  clover  and 
legumes. 

THE  ORGANIC  COMPOUNDS  OF  SOILS 

i oi   Sources  of  the  Organic  Compounds  of  Soils.— 

The  organic  compounds  of  soils  are  composed  of  the 
elements  carbon,  hydrogen,  oxygen,  and  nitrogen. 
When  vegetable  and  animal  matter  undergo  decay  in 
contact  with  the  soil,  compounds  as  carbon  dioxide, 
water,  ammonia,28  organic  acids,  and  various  derivatives 
are  formed,  while  some  of  the  organic  acids  unite  with 
the  mineral  matter  of  the  soil  to  form  humates. 
Micro-organisms  take  an  important  part  in  the  decay 
of  animal  and  vegetable  matter  and  the  production  of 
organic  compounds  in  soils.  In  some  soils,  the  or- 
ganic compounds  of  plants,  as  cellulose,  proteids,  and 
carbohydrates  like  pentosans,  are  present,  while  in 
other  soils  these  compounds  have  undergone  partial 
oxidation.  Some  authorities  claim  (see  Section  137) 
that  a  portion  of  the  initial  organic  matter  of  soils  is 
the  result  of  the  workings  of  carbon  assimilating 
nitro-organisms.  The  main  source  of  the  soil's  or- 
ganic matter,  however,  is  the  accumulated  animal  and 
vegetable  remains  which  exist  in  various  stages  of 
decay.  The  organic  matter  of  soils  is  a  mechanical 
mixture  of  a  large  number  of  organic  compounds, 
many  of  which  have  not  as  yet  been  studied. 

102.  Classification  of  the  Organic  Compounds. — 
Various  attempts  have  been  made  to  classify  the  or- 


HUMIFICATION   AND    HUMATKS  87 

ganic  compounds  of  the  soil,  but  those  which  have 
been  described  are  without  doubt  mixtures  of  various 
bodies,  and  not  distinct  compounds.  An  old  classifi- 
cation by  Miilder29  was  humic,  ulmic,  crenic,  and  ap- 
procrenic  acids.  This  classification  does  not  include 
any  nitrogenous  matter  containing  more  than  4  per 
cent,  nitrogen,  while  organic  matter  with  8  to  10  per 
cent,  and  in  some  cases  18  per  cent,  of  nitrogen  is 
quite  frequently  met  with  ;  hence  this  classification  is 
incomplete  as  it  includes  only  a  part  of  the  organic 
compounds  of  the  soil.  For  practical  purposes  the 
organic  compounds  of  soils  may  be  divided  into  three 
classes  :  (i)  Those  of  low  nitrogen  content,  i  to  4  per 
cent,  of  nitrogen ;  (2)  medium  nitrogen  content,  5  to 
10  per  cent. ;  (3)  high  nitrogen  content,  n  to  20  per 
cent. 

103.  Humus. — The   term    humus   is   employed  to 
designate  the  most  active  parts  of  the  organic  com- 
pounds.    Humus  is  the  animal  and  vegetable  matter 
of  the  soil  in   intermediate  forms  of  decomposition. 
From  different  soils,  it  is  extremely  varied   in   compo- 
sition ;  in  one  soil  it  may  have  been  derived  mainly 
from  cellulose,  while  in  another  it  may  have  been  de- 
rived from  a  mixture  of  cellulose,  proteid  bodies,  and 
other  organic  compounds.     The   term  humus,  unless 
qualified,  is  a  very  indefinite  one.  The  humus  as  given 
in  the  analyses  of  soils  is  obtained  by  extracting  the 
soil    with    a  dilute  alkali  as    ammonium  hydroxide, 
after  treating  the  soil  with  a  dilute  acid  to  remove  the 
lime  which  renders  the  humus  insoluble. 

104.  Humification  and  Humates. — When  the  ani- 


88  SOILS   AND    FERTILIZERS 

mal  and  vegetable  matter  incorporated  with  soils  un- 
dergoes decomposition  there  is  a  union  of  some  of  the 
organic  compounds  with  the  base-forming  elements  of 
the  soil.  The  decaying  organic  matter  produces  or- 
ganic products  of  an  acid  nature.  The  organic  acids 
and  the  base-forming  products  unite  to  form  humates 
or  organic  salts,  which  are  neutral  bodies.  This 
process  is  humification.17 

Humic  acid  -j-  calcium  carbonate  =  calcium  humate  +  CO2. 
Humic  acid  -)-  potassium  sulphate  —  potassium  humate,  etc. 

The  fact  that  a  union  occurs  between  the  organic 
matter  and  the  soil  has  been  demonstrated  by  mixing 
with  soils  known  amounts  of  various  organic  mate- 
rials, as  cow  manure,  green  clover,  meat  scraps,  and 
sawdust,  and  allowing  humification  to  go  on  for  a  year 
or  more.  After  humification  has  taken  place,  the 
humus  extracted  from  the  soil  contains  more  potash, 
phosphoric  acid,  and  other  elements  than  were  present 
in  the  humus  of  the  original  soil  and  humus-forming 
material,  showing  that  a  chemical  union  has  taken 
place  between  the  decaying  organic  matter  and  the  soil. 
The  power  of  various  organic  substances  to  produce 
humates  is  illustrated  in  the  following  table.  29>  8s 

Humic  phos-  Humic 

phoric  acid.  potash. 

Cow  manure  humus  :  Grams.  Grams. 

In  original  manure  and  soil 1.17  1.06 

In  final  humus  product  (after  hu- 
mification)    1.62  1.27 

Gain  in  humic  forms 0.45  0.21 

Green  clover  humus : 

In  original  soil  and  clover 3.21  5.26 

In  final  humus  product 3.74  4.93 

Gain  in  humic  forms 0.53      (Loss)  0.33 


VALUE   AND    COMPOSITION   OF    HUMATES  89 

Humic  phos-  Humic 

phoric  acid.  potash. 

Meat  scrap  humUS :  Grams.  Grams. 

In  original  meat  scraps  and  soil-  •  •   1.07  0.25 

In  final  humus  product 1.18  0.36 

Gain o.n  o.n 

Sawdust  humus : 

In  original  sawdust  and  soil 0.85  0.67 

In  final  humus  product 0.78  0.70 

Oat  straw  humus  : 

In  original  straw  and  soil  •    1.02  2.42 

In  final  humus  product 1.03  2.41 

105.  Comparative  Value  and  Composition  of  Hu- 
mates.  —  The  humus  produced  from  nitrogenous 
bodies  as  meat  scraps,  is  more  valuable  than  that  pro- 
duced from  cellulose  bodies,  as  sawdust,  because  the 
former  has  greater  power  of  combining  with  the 
phosphoric  acid  and  potash  of  the  soil.  The  non- 
nitrogenous  compounds,  as  cellulose,  starch,  and  sugar, 
undergo  fermentation  but  seem  to  possess  little,  if  any, 
power  to  form  tuimates.  There  is  also  a  great  differ- 
ence in  soils  as  to  their  humus-producing  powers. 
Soils  deficient  in  lime  or  alkaline  compounds  possess 
only  a  feeble  power  to  produce  humates.  There  is 
also  a  marked  variation  in  the  composition  of  the 
humus  produced  from  different  kinds  of  organic  matter. 
Straw,  sawdust,  and  sugar,  materials  rich  in  cellulose 
and  other  carbo-hydrates,  yield  a  humus  characteris- 
tically rich  in  carbon  and  poor  in  nitrogen.  Materials 
rich  in  nitrogen,  like  meat  scraps,  green  clover,  and 
manure,  produce  a  more  valuable  humus,  rich  in  nitro- 
gen and  possessing  the  power  to  combine  with  the 


90  SOILS    AND    FERTILIZERS 

potash  and  phosphoric  acid  of  the  soil  to  form  hu- 
mates. 

COMPOSITION  OF  HUMUS  PRODUCED  BYSO 

Cow       Green      Meat      Wheat       Oat  Saw- 
manure,  clover,    scraps,     flour.      straw.  dust.      Sugar 

Carbon 41.95     54.22     48.77     51.02     54.30  49.28     57.84 

Hydrogen 6.26       3.40       4.30       3.82       2.48  3.33       3.04 

Nitrogen 6.16       8.24     10.96       5.02       2.50  0.32       0.08 

45-63     34-14     35-97     40.14    40.72  47-°7    39-°4 


Total 100.00  100.00  100.00  100.00  100.00  IOD.OO  100.00 

Highest.  Lowest.  Difference. 

Carbon 57.84  41.95  15.89 

Hydrogen    6.26  2.48  3.78 

Nitrogen 10.96  0.08  10.88 

Oxygen 47.07  34.14  12.93 

Variations  in  composition  are  noticeable.  The 
humus  produced  from  each  material  as  green  clover, 
oat  straw,  or  sawdust,  is  different  from  that  produced 
from  any  other  material.  The  humus  from  green 
clover  is  very  complex  in  nature.  It  contains  both 
nitrogenous  and  non-nitrogenous  compounds,  and 
each  class  has  a  different  action  in  humification 
processes,  hence  it  follows  that  the  humus  from  the 
green  clover  must  be  a  complex  mixture  of  both 
nitrogenous  and  non-nitrogenous  bodies. 

The  nature  of  the  humus,  whether  nitrogenous  or 
non-nitrogenous,  is  important.  Humus  produced  from 
sawdust  and  humus  from  meat  scraps  may  be  taken 
respectively  as  types  of  non-nitrogenous  and  nitroge- 
nous humus. 

106.  Value  of  Humates  as  Plant  Food. — Various 
opinions  have  been  held  regarding  the  actual  value, 
as  plant  food,  of  this  product  from  partially  decayed 
animal  and  vegetable  matter.  Humus  was  formerly 
regarded  as  composed  only  of  carbon,  hydrogen,  and 


VALUE   OF   HUMATES   AS   PLANT   FOOD  9 1 

oxygen,  and  inasmuch  as  plants  obtain  these  elements 
from  water  and  from  the  carbon  dioxide  of  the  air, 
no  value  was  assigned  to  humus.  Later,  investigators 
added  nitrogen  to  the  list,  but  stated  that  the  nitrogen, 
when  combined  with  the  humus  and  before  under- 
going fermentation,  was  of  no  value  as  plant  food. 

Recent  investigations  have  proved  that  the  phos- 
phoric acid  and  other  mineral  elements  combined 
with  the  organic  matter  of  soils  are  of  value  as  plant 
food,17  and  it  has  been  demonstrated  that  crops  grown 
on  the  black  soils  of  Russia  obtain  a  large  part  of 
their  mineral  food  from  organic  combinations.84.  Cul- 
ture experiments  have  shown  that  under  normal  con- 
ditions plants  like  oats  and  rye  may  obtain  their  min- 
eral food  entirely  from  humate  sources.  Seeds  when 
planted  in  a  mixture  of  pure  sand  and  neutral  humates 
from  fertile  soils,  produced  normal  plants.  In  order  to 
secure  the  best  conditions  for  growth,  a  little  lime 
must  be  present  to  prevent  the  formation  of  humic 
acid,  and  the  organisms  found  in  fertile  fields  must 
also  be  introduced.  The  following  example  is  given 
of  oats  which  were  grown  when  the  only  supply  of 
mineral  food  was  in  humate  forms. 

NITROGEN  AND  ASH  ELEMENTS.17 

In. six  oat  In  six  mature 

seeds.  plants. 

Gram.  Gram. 

Nitrogen 0.0040  0.0556 

Potash 0.0013  0.0640 

Soda o.ooor  0.0079 

Lime 0.0002  0.0249 

Magnesia 0.0005  o.oi  10 

Iron    0.0064 

Phosphoric  anhydride 0.0016  0.0960 

Sulphuric  anhydride o.ooor  0.0090 

Silicon 0.0026  0.7300 


92  SOILS   AND   FERTILIZERS 

The  fact  that  plants  feed  on  humate  compounds 
and  that  decaying  animal  and  vegetable  matter  pro- 
duce humates  from  the  inert  potash  and  phosphoric 
acid  of  the  soil,  has  an  important  bearing  upon  crop 
production,  because  it  indicates  a  way  by  which  inert 
plant  food  may  be  converted  into  more  active  and 
available  forms.  It  also  explains  that  stable  manure 
is  valuable  because  it  makes  the  inert  plant  food  of  the 
soil  more  available. 

107.  Amount  of  Plant  Food  in  Humate  Forms. — 
In  a  prairie  soil  containing  3  y2  per  cent,  of  humus 
there  are  present  100,000  pounds  of  humus  per  acre. 
Combined  with  this  humus  there  are  from  1,000  to 
1,500   pounds   each    of   phosphoric  acid  and  potash. 
Similar  soils  which  have  been  under  long  cultivation 
without  the  restoration  of  any  humus  contain  from 
300  to  500  pounds  each  of  humic  potash   and   phos- 
phoric acid.18     A  decline  in  crop-producing  power  has 
in   many   cases  been  brought  about   by    the   loss  of 
humus. 

108.  Loss  of  Humus. — Loss  of  humus  from  soils 
is  caused  by  oxidation  and  by  fires.     Any  method  of 
cultivation  which   accelerates  oxidation  reduces  the 
humus  content.     In  many  of  the  western  prairie  soils 
which  have  been  under  continuous  grain  cultivation 
for  thirty  years  or   more,  the  amount  of  humus  has 
been  reduced  one-half.     Summer  fallowing  also  causes 
a  loss  of  humus.     When  land  is  continually  under  the 
plow,  and  no  manures  are  used,  the  humus  is  rapidly 
oxidized,  and  there  is  left,  in  the  soil,  organic  matter 
which  is  slow  to  decay. 

Forest  and  prairie  fires  have  been  very  destructive 


PHYSICAL  PROPERTIES  OF  SOILS,  ETC.  93 

to  the  organic  compounds  of  the  soil.  A  soil  from 
Hinckley,  Minn.,  before  the  great  forest  fire  of  1893, 
showed  1.69  per  cent,  humus  and  0.12  per  cent,  nitro- 
gen.18 After  the  fire  there  were  present  0.41  per  cent, 
humus  and  0.03  per  cent,  nitrogen.  The  forest  fire 
caused  a  loss  of  2,500  pounds  of  nitrogen  per  acre. 
In  clearing  new  land1,  particularly  forest  land,  there  is 
frequently  an  unnecessary  destruction  of  humus  mate- 
rials. Instead  of  burning  all  the  vegetable  matter 
it  would  be  better  economy  to  leave  some  in  piles  for 
future  use  as  manure.  When  all  of  the  vegetable 
matter  has  been  burned,  two  or  three  good  crops  are 
obtained,  but  the  permanent  crop-producing  power  of 
the  land  is  reduced  because  of  the  loss  of  nitrogen  and 
humus.  When  the  vegetable  matter  has  been  only 
partially  removed,  the  crops  at  first  may  be  smaller, 
but  in  a  few  years  returns  will  be  greater  than  if  all 
of  the  vegetable  matter  had  been  burned. 

109.  Physical  Properties  of  Soils  Influenced  by 
Humus.  —  The  physical  properties  of  a  soil  may  be 
entirely  changed  by  the  addition  or  the  loss  of  humus. 
The  influence  of  humus  upon  the  weight,  color,  heat, 
and  water-retaining  power  of  soils  is  discussed  in  the 
chapter  on  the  physical  properties  of  soils.  Soils  re- 
duced in  humus  content  have  less  power  of  storing  up 
water  and  resisting  drought.  This  fact  is  illustrated 
in  the  following  table  : 31 

PER  CENT.  WATER. 

After  10  hours 

exposure  in 
In  soil.       tray,  to  sun. 

Soil  rich  in  humus  (3.75  per  cent.) 16.48  6.12 

Adjoining  soil  poorer  in  humus  (2. 50  percent.)   12.14  3-94 


94 


SOILS   AND    FERTILIZERS 


no.  Humic  Acid. — In  the  absence  of  calcium  car- 
bonate or  other  alkaline  compounds,  the  vegetable 
matter  may  produce  acid  products  destructive  to  the 
growth  of  some  crops.  The  acidity  in  such  cases  can 
be  readily  corrected  by  the  use  of  lime  or  wood  ashes. 
Acid  soils  can  be  distinguished  by  their  action  upon 
blue  litmus  paper.  A  soil  may,  however,  give  an  acid 
reaction  and  contain  a  fair  amount  of  lime  as  a  silicate. 
The  subject  of  acid  soils  and  liming  is  considered  in 
Chapter  IX.  Studies  conducted  by  the  Rhode  Island 
Experiment  Station  indicate  that  the  areas  of  acid 
soils  are  quite  extensive. 

in.  Soils  in  Need  of  Humus. — Sandy  and  sandy 


Fig.  20.     Hunris  from  old  scil. 


Fig.  21.     Humis  from  new  soil. 

loam  soils  that  have  been  cultivated  for  a  number  of 
years  to  corn,  potatoes,  and  small  grains  without  rota- 
tion of  crops  or  the  use  of  stable  manures,  are  deficient 
in  humus.  Clay  soils,  as  a  rule,  do  not  stand  in  need 
of  humus  so  much  as  loam  and  sandy  soils.  The  me- 


DIFFERENT   METHODS   OF   FARMING,    ETC.  95 

chanical  condition  of  heavy  clays  is,  however,  im- 
proved by  the  addition  of  humus-forming  material. 
The  addition  of  humus  to  loam  or  sandy  soils  is  bene- 
ficial in  preventing  the  soil  from  drifting,  because  it 
binds  together  the  soil  particles.  There  are  but  few 
arable  soils,  under  ordinary  cultivation,  to  which  it  is 
not  safe  to  add  humus-forming  materials,  either  alone 
or  jointly  with  lime.  Ordinary  prairie  soils,  for  the 
first  ten  years  after  breaking,  are  usually  well  supplied. 
Swampy,  peaty,  and  muck  soils  contain  large  amounts, 
in  fact,  they  are  often  overstocked.  "Alkali"  soils 
are  usually  deficient  in  humus. 

112,  Active  and  Inactive  Humus. — When  soil  has 
been  long  under  cultivation,  and  no  manures  have 
been  used,  the  nitrogen  and  mineral  matters  combined 
with  the  humus  are  reduced.  The  humus  from  long- 
cultivated  fields  contains  a  higher  per  cent,  of  carbon 
than  that  from  well-manured  or  new  land  ;  it  is  also 
less  active  because  of  the  higher  per  cent,  of  carbon 
which  does  not  readily  undergo  oxidation.18 


Humus  from 
new  soil. 
Per  cent. 

Humus  from 
old  soil. 
Percent. 

50.10 
4.80 
33-70 
6.50 
A.QO 

Oxv^en  •  • 

.    ^  1  6 

8  12 

Ash.. 

6.60 

Total  humus  material..     5.30  3.38 

113.  Influence  of  Different  Methods  of  Farming  upon 
Humus. — The  system  of  farming  has  a  direct  effect 
upon  the  humus  content  and  the  composition  of  the 


96  SOILS   AND    FERTILIZERS 

soil.  Where  live  stock  is  kept,  the  manure  judiciously 
used,  and  the  crops  systematically  rotated,  the  crop- 
producing  power  of  the  land  is  not  decreased,  as  in  the 
case  of  the  one-crop  system.  The  influence  of  differ- 
ent systems  of  farming  upon  the  humus  content  and 
other  properties  of  the  soil  may  be  observed  in  the 
following  table  :  3I 


S-8 

bee 


Character  of  soil.  ^p^          Sp,  £01          PL,O,C&. 

Cultivated  thirty-five  years  ; 
rotation  of  crops  and  ma- 
nure ;  high  state  of  pro- 
ductiveness    70  3.32  0.30  0.04  48 

Originally  same  as  i  ;  con- 
tinuous grain  cropping  for 
thirty-five  years ;  low  state 
of  productiveness 72  1.80  0.16  o.oi  39 

Cultivated  forty-two  years  ; 
systematic  rotation  and 
manure  ;  good  state  of  pro- 
ductiveness    70  3.46  0.26  0.03  59 

Originally  same  as  3  ;  culti- 
vated thirty-five  years  ;  no 
systematic  rotation  or  ma- 
nure ;  medium  state  of 
productiveness 67  2.45  0.21  0.03  57 


CHAPTER  IV 


NITROGEN   OF   THE   SOIL   AND   AIR,    NITRIFICATION,  AND 
NITROGENOUS  MANURES 

114.    Importance  of   Nitrogen  as   Plant  Food. — 

The  illustration  (Fig.  22)  shows  an  oat  plant  which  re- 
ceived no  nitrogen,  while  potash,  phosphates,  lime,  and 
all  other  essential  elements  of  plant  food 
were  liberally  supplied.  Observe  the  pe- 
culiar and  restricted  growth,  with  but 
limited  root  development.  The  leaves 
were  yellowish. 

In  the  absence  of  nitrogen  a  plant 
makes  no  appreciable  growth.  With  only 
a  limited  supply,  a  plant  begins  its  growth 
in  a  normal  way,  but  as  soon  as  the  avail- 
able nitrogen  is  used  up,  the  lower  and 
smaller  leaves  begin  gradually  to  die 
down  from  the  tips,  and  all  of  the  plant's 
energy  is  centered  in  one  or  two  leaves. 
In  one  experiment  when  only  a  small 
amount  of  nitrogen  was  supplied,  the  plant 
struggled  along  in  this  way  for  about  nine 
weeks,  making  a  total  growth  of  but  six 
and  one-half  inches.16  Just  at  the  critical  point 
when  the  plant  was  dying  of  nitrogen  starvation, 
a  few  milligrams  of  calcium  nitrate  were  given.  In 
thirty-six  hours  the  plant  showed  signs  of  renewed 
life,  the  leaves  assumed  a  deeper  green,  a  new  growth 
was  begun,  and  finally  four  seeds  were  produced. 

(7) 


Fig.  22. 
Oat   plant 
grown  with- 
out nitrogen. 


9§  SOILS   AND   FERTILIZERS 

During  the  time  of  seed  formation  more  nitrogen  was 
added,  but  with  no  beneficial  result.  All  of  the  es- 
sential elements  for  plant  growth  were  liberally  pro- 
vided, except  nitrogen,  which  was  very  sparingly  sup- 
plied at  first,  until  near  the  period  of  seed  formation, 
when  it  was  more  liberally  supplied. 

When  plants  have  reached  a  certain  period  in  their 
development,  and  have  been  starved  for  want  of  nitro- 
gen, the  later  application  of  this  element  does  not 
produce  normal  growth,  as  the  energies  of  the  plant 
have  been  used  up  in  searching  for  food.  Nitrogen, 
as  well  as  potash,  lime,  and  phosphoric  acid,  are  all 
necessary  while  plants  are  in  their  first  stages  of 
growth. 

In  the  case  of  wheat,  nitrogen  is  assimilated  more 
rapidly  than  are  any  of  the  mineral  elements.  Before 
the  plant  heads  out,  over  85  per  cent,  of  the  total 
nitrogen  required  has  been  taken  from  the  soil.36 
Corn  also  takes  up  all  of  its  nitrogen  from  four  to 
five  weeks  before  the  crop  matures.  Flax  takes  up  75 
per  cent,  of  its  nitrogen  during  the  first  fifty  days  of 
growth.38 

Nitrogen  is  demanded  by  all  crops.  It  forms  the 
chief  building  material  for  the  proteids  of  plants.  In 
the  absence  of  a  sufficient  amount  of  nitrogen,  the 
rich  green  color  is  not  developed  ;  the  foliage  is  of  a 
yellowish  tinge.  Nitrogen  is  one  of  the  constituents 
of  chlorophyl,  *the  green  coloring-matter  of  plants, 
hence  when  there  is  a  lack  of  nitrogen  only  a  limited 
amount  of  chlorophyl  can  be  produced.  Plants  with 


ATMOSPHERIC   NITROGEN  99 

large,  well-developed  leaves  of  a  rich  green  color  are 
not  suffering  for    nitrogen.      Nitrogenous   fertilizers 
have  a  tendency  to  produce  a  luxurous  growth  of 
foliage,  deep  green  in  color. 
ATMOSPHERIC  NITROGEN  AS   A  SOURCE  OF  PLANT  FOOD 

115.  Early  Views. — In  addition  to  carbon,  hydro- 
gen, and  oxygen,  which  form  the  organic  compounds 
of  plants,  it  was  known  as  early  as  the  beginning  of 
the  present  century  that  plants  also  contained  nitrogen. 
The  sources  of  the  carbon,  hydrogen,  and  oxygen  for 
crop  purposes   were   much  easier  to   determine  and 
understand   than  the  sources  of  nitrogen.     Priestley, 
the  discoverer  of  oxygen,  believed  that  the  free  nitro- 
gen of  the  air  was  a  factor  in  supplying  plant  food. 
De  Saussure  arrived  at  just  the  opposite  conclusion. 
Neither  of  these  assumptions  were  convincing  because 
methods  of  chemical  analysis  had  not  yet  been  suffi- 
ciently perfected  to  solve  the  question.39 

116.  Boussingault's  Experiments.  —  Boussingault 
was  the  first  to  make  a  careful  study  of  the  subject. 
In  a  prepared  soil,  free  from  nitrogen,  and  containing 
all  of  the  other  elements  necessary  for  plant  growth, 
he  grew  clover,  wheat,  and  peas,  carefully  determining 
the  nitrogen  in  the  seed.     The  plants  were  allowed 
free  access  to  the  air,  being  simply   protected  from 
dust,  and  were  watered    with    distilled   water.     But 
little  growth   was   made.     At  the  end  of  two  months 
the  plants  were  submitted  to  chemical  analysis,  and 
the  amount  of  nitrogen  present  was  determined. 

His  first  results  are  given  in  the  following  table  :  4° 


IOO 


SOILS    AND    FERTILIZERS 


NITROGEN. 

In  seed  sown.      In  plant.  Gain. 

Gram.  Gram.  Gram. 

Clover,  2  nios o.  n  0.12  o.oi 

"         3  "     0.114  0.156  0.042 

Wheat,  2  "     0.043  °-°4  — 0.003 

"        3  "     0.057  0.06  0.003 

Peas,      2  "     0.047  o.io  0.053 

Boussingault  concluded  that  when  plants  in  a  sterile 
soil  were  exposed  to  the  air,  there  was  with  some  a 
slight  gain  of  nitrogen,  but  the  amount  gained  from 
atmospheric  sources  was  not  suffi- 
cient to  feed  the  plant  and  allow  it 
to  reach  full   maturity.     By  many 
these  results  were  not  accepted  as 
conclusive. 

Fifteen  years  later  (1853)  Bous- 
singault repeated  his  experiments, 
but  in  a  different  way.  The  plants 
were  now  grown  in  a  large  carboy 
with  a  limited  volume  of  air  so  as  to 
cut  off  all  sources  of  combined  nitro- 
gen, as  ammonia.  By  means  of  a 
second  glass  vessel  (b,  Fig.  23)  the 
carboy  was  kept  liberally  supplied 
with  carbon  dioxide,  so  that  plant 
growth  would  not  be  checked  for  lack  of  this  material. 
When  experiments  were  carried  on  in  this  way  using  a 
fertile  soil,  the  plants  reached  full  maturity,  but  when 
a  soil  free  from  nitrogen  was  used,  plant  growth  was 
soon  checked.  A  general  summary  of  this  work  is 
given  in  the  following  table  :4° 


Fig.  23. 

Plants  grown 

in  carboy. 


ATMOSPHERIC   NITROGEN  IOI 

NITROGEN. 

In  seeds.  In  plant.  Loss. 

Gram.  Gram.  Gram. 

Dwarf  beans o.  1001  0.0977  — 0.0024 

Oats 0.0109  0.0097  — 0.0012 

White  lupines 0.2710  0.2669  — 0.0041 

Garden  cress 0.0013  0.0013  

These  experiments  show  that  with  a  sterilized  soil, 
and  all  sources  of  combined  atmospheric  nitrogen  cut 
off,  the  free  nitrogen  of  the  air  takes  no  part  in  the 
food  supply  of  the  plant. 

In  1854  Boussingault  again  repeated  his  experi- 
ments on  nitrogen  assimilation.  This  time  he  grew 
the  plants  in  a  glass  case  so  constructed  that  there  was 
a  free  circulation  of  air  from  which  all  combined  nitro- 
gen had  been  removed.  These  experiments  were 
similar  to  his  second  series;  the  plants,  however, 
were  not  grown  in  a  limited  volume  of  air.  The 
results  obtained  showed  that  the  free  nitrogen  of 
the  air,  under  the  conditions  of  the  experiment,  took 
no  part  in  the  food  supply  of  the  plants.  If  anything, 
there  was  less  nitrogen  recovered  in  the  dwarfed 
plants  than  there  was  in  the  seed  sown. 

117.  Ville's  Results. — About  the  same  time  Ville 
carried  on  a  series  of  experiments  of  like  nature,  but 
in  a  different  way,  and  arrived  at  just  the  opposite 
conclusions.  In  short,  his  experiments  indicated  that 
plants  are  capable  of  making  liberal  use  of  the  free 
nitrogen  of  the  air  for  food  purposes.  The  directly 
opposite  conclusions  of  Boussingault  and  Ville,  led  to 
a  great  deal  of  controversy.  The  French  Academy  of 
Science  took  up  the  question,  and  appointed  a  com- 


102  SOILS   AND    FERTILIZERS 

mission  to  review  the  work  of  Ville.  The  commis- 
sion consisted  of  six  prominent  scientists.  They 
reported  that  UM.  Ville's  conclusions  are  consistent 
with  his  labor  and  results."39 

118.  Work  of  Lawes  and  Gilbert. — A  little  later 
L,awes   and   Gilbert   carried   on    such   extensive   ex- 
periments under  a  variety  of  conditions  as  to  remove 
all  doubt  regarding  the  question.     Plants  were  grown 
in  sterilized  soils,  in  prepared  pumice  stone,  and  in 
soils  with  a  limited  and  known  quantity  of  nitrogen 
beyond  that  contained  in  the  seed.     Different  kinds 
of  plants  were  experimented  with.     The  work  was 
carried  on  with   the   utmost  care  and  with  apparatus 
so  constructed  as  to  eliminate  all  disturbing  factors. 
The   results   in  the  aggregate   clearly   indicate   that 
plants,  when  acting  in  a  sterile  medium,  are  unable 
to  make  use  of  the  free  nitrogen  of  the  air  for  the  pro- 
duction of  organic  matter.39. 

119.  Atwater's  Experiments. — Atwater  carried  on 
similar  experiments  in  this  country.41      His    results 
indicate    that    when   seeds    germinate   they    lose    a 
small  part  of  their  nitrogen,  and   that  when  legumes 
are  grown  in   a  sterile  soil,  but  are  subsequently  ex- 
posed to  the  air,  a  fixation  of  nitrogen  may  occur. 

120.  Field  and  Laboratory  Tests. — By  a  five  years' 
rotation  of  clover  and  other  leguminous  plants,  Lawes 
and  Gilbert  found  tha4:  a  soil  gained  from  two  to  four 
hundred  pounds  of  nitrogen  per  acre,  in  addition  to 
that  removed  in  the  crop,  while  land  which  produced 
wheat  continuously  had  gradually  lost  nitrogen.    The 


ATMOSPHERIC   NITROGEN  103 

amount  in  the  subsoil  remained  nearly  the  same.  All 
of  these  facts  plainly  indicated  that  crops  like  clover 
had  the  power  of  gaining  nitrogen  from  unknown 
sources.  The  results  of  prominent  German  agricul- 
turists led  to  the  same  conclusion.  It  was  known 
that  wheat  grown  after  clover  gave  as  good  results  as 
the  use  of  nitrogenous  manures  for  the  wheat,  but  for 
many  years  this  fact  was  unexplained. 

Laboratory  experiments  with  sterilized  soils  do  not 
represent  the  normal  conditions  of  growing  crops 
where  all  of  the  bacteriological  agencies  of  the  soil, 
the  air,  and  the  plant,  are  free  to  act.  Experiments 
have  shown  that  these  agencies  have  an  important 
bearing  upon  plant  growth. 

In  the  work  of  the  different  investigators  prior  to 
1888,  plants  were  grown  mainly  in  sterilized  soils,  and 
under  such  conditions  they  were  unable  to  make  use 
of  the  free  nitrogen  of  the  air,  except  when  subse- 
quently innoculated  from  the  air. 

121.  Hellriegel's  Experiments. — Hellriegel  grew 
leguminous  plants  in  nitrogen-free  soils.  One  set  of 
plants  was  watered  with  distilled  water,  while  another 
had  in  addition  small  amounts  of  leachings  from  an 
old  loam  field.  The  plants  watered  with  distilled 
water  alone,  made  but  little  growth,  while  those 
watered  with  the  loam  leachings  reached  full  matur- 
ity and  contained  something  like  a  hundred  times 
more  nitrogen  than  was  in  the  seed  sown.  The  dark 
green  color  was  also  developed,  showing  the  presence 
of  a  normal  amount  of  chlorophyl.  The  roots  of  the 


104  SOILS   AND   FERTILIZERS 

plants  had  well-formed  swellings  or  nodules,  while 
those  that  were  watered  with  distilled  water  alone  had 
none.  The  loam  leachings  contained  only  a  trace  of 
nitrogen.42 

122.  Experiments  of  Wilfarth. — Experiments  by 
Wilfarth  give  more  exact  data  regarding  the  amount 
of  nitrogen  taken  from  the  air.    Two  plots  of  lupines 
were  grown,   one  was  watered  with  distilled   water, 
while   the  other  received  in  addition  leachings  from 
an  old  lupine  field. 

Watered  with  distilled  water.  Watered  with  soil  leachings. 

Dry  matter.  Nitrogen.  Dry  matter.  Nitrogen. 

Grams.  Grams.  Grams.  Grams. 

0.919  0.015  44-72  1-099 

0.800  0.014  45-6i  i  .153 

0.921  0.013  4448  I-I95 

i. 021  0.013  42.45  T-337 

These  experiments  have  been  verified  by  many 
other  investigators  until  the  fact  has  been  established 
that  leguminous  plants  may,  through  the  agency  of 
micro-organisms,  make  use  of  the  free  nitrogen  of  the 
air.  The  work  of  Hellriegel  was  not  accidental  but 
the  result  of  careful  and  systematic  investigation.  As 
early  as  1863  he  observed  that  clover  would  develop 
along  the  roadway  in  sand  in  which  there  was  scarcely 
a  trace  of  combined  nitrogen. 

123.  Composition    of    Root    Nodules. — The    root 
nodules  referred  to,  are  particularly  rich  in  nitrogen. 
In  one  experiment,  the  light-colored  and  active  ones 
contained  5.55  per  cent.,  while  the  dark-colored  and 
older   ones   contained    3.21    per   cent.       The    entire 
nodules  of  the  root,  both   active  and  inactive,  con- 


ATMOSPHERIC    NITROGEN  105 

tained  4.60  per  cent,  nitrogen.  The  root  itself  con- 
tained 2.21  per  cent.43 

The  root  nodules  also  contain  definite  and  charac- 
teristic micro-organisms,  and  it  was  the  spores  of  these 
organisms  that  were  present  in  the  soil  extract  in  both 
Hellriegel's  and  Wilfarth's  experiments.  In  the  ster- 
ilized soils  they  were  not  present.  These  organisms 
found  in  root  nodules,  are  the  essential  agents  which 
aid  in  the  fixation  of  the  free  nitrogen  of  the  air,  and 
in  its  ultimate  use  as  plant  food.  Experiments  have 
shown  that  these  organisms  are  capable  of  being 
propogated  in  nutritive  media,  separate  from  clover 
roots.87 

124.  Nitrogen  in  the  Root  Nodules  Returned  to 
the  Soil. — Ward  has  shown  that  when  clover  roots 
decay,  the  organisms  and  nitrogen  present  in  the 
nodules  are  distributed  within  the  soil.38  Hence, 
whenever  a  leguminous  crop  is  raised,  nitrogen  is 
added  to  the  soil,  instead  of  being  taken  away,  as  in 
the  case  of  a  grain  crop.  The  amount  of  nitrogen 
per  acre  returned  to  the  soil  by  a  leguminous  crop  as 
clover,  varies  with  the  growth  of  the  crop.  In  the 
roots  of  a  clover  crop  a  year  old  there  are  present 
from  20  to  30  pounds  of  nitrogen  per  acre,  while  in 
the  roots  and  culms  of  a  dense  clover  sod,  two  or  three 
years  old,  there  may  be  present  75  pounds  or  more  of 
nitrogen.  Peas,  beans,  lucern,  cow  peas,  and  all 
legumes,  possess  the  power  of  fixing  the  free  nitrogen 
of  the  air  by  means  of  micro-organisms.  The  micro- 
organisms associated  with  one  species,  as  clover,  differ 


106  SOILS   AND   FERTILIZERS 

from  those  associated  with  another,  as  lucern.  The 
amount  of  nitrogen  which  the  various  legumes  return 
to  the  soil  is  variable.  Hellriegel's  results  are  of  the 
greatest  importance  to  agriculture,  because  they  show 
how  the  free  nitrogen  of  the  air  can  be  utilized  in- 
directly as  food  by  crops  unable  to  appropriate  it  for 
themselves. 

THE  NITROGEN  COMPOUNDS  OF  THE  SOIL 

125.  Origin  of  the  Soil  Nitrogen. — The  nitrogen  of 
the  soil  is  derived  chiefly  from  the  accumulated  re- 
mains of  animal  and  vegetable  matter.     The  original 
source  of  the  soil  nitrogen,  that  is  the  nitrogen  which 
furnished  food  to  support  the  vegetation  from  which 
our  present  stock  of  soil  nitrogen  'is  obtained,  was 
probably  the  free  nitrogen  of  the  air.     All  of  the  ways 
in  which  the  free  nitrogen  of  the  air  has  been  made 
available  to  plants  of  higher  orders   which  require 
combined  nitrogen,  are  not  known.     It  is  supposed, 
however,   that  this  has  been  brought  about  by  the 
workings  of  lower  forms  of  plant  life,  and  by  micro- 
organisms.    Whatever  these  agencies  have  been  they 
do  not  appear  to  be  active  in  a  soil   under  high  culti- 
vation, because  the  tendency  of  ordinary  cropping  is 
to  reduce  the  supply  of  soil  nitrogen. 

126.  Organic  Nitrogen  of  the  Soil. — In   ordinary 
soils  the  nitrogen  is  present  mainly  in  organic  forms 
combined   with   the  carbon,   hydrogen,  and  oxygen, 
and  to  a  less  extent  with  the  mineral  elements,  form- 
ing  nitrates.     The  organic  forms  of  nitrogen,   it  is 
generally  considered,  are  incapable  of  supplying  plants 


NITROGEN    COMPOUNDS   OF   THE   SOU,  1 07 

with  nitrogen  for  food  purposes  until  the  process 
known  as  nitrification  takes  place.  The  nitrogenous 
organic  compounds  in  cultivated  soils  are  derived 
mainly  from  the  undigested  protein  compounds  of 
manure  and  from  the  nitrogenous  compounds  in  crop 
residues,  and  are  present  mainly  as  insoluable  pro- 
teids.85  When  decomposition  occurs,  arnides,  organic 
salts,  and  other  allied  bodies  are  without  doubt  pro- 
duced as  intermediate  products  before  nitrification 
takes  place.  The  organic  nitrogen  of  the  soil  may  be 
present  in  exceedingly  inert  forms  similar  to  leather. 
In  fact,  in  many  peaty  soils  there  are  large  amounts  of 
inactive  organic  compounds  rich  in  nitrogen.  In 
other  soils  the  nitrogen  is  present  in  less  complex 
forms.  The  organic  nitrogen  of  the  soil  may  vary  in 
complexity  from  forms  like  the  nitrogen  of  urea  to 
forms  like  that  of  peat. 

127.  Amount  of  Nitrogen  in  Soils. — The  fertility 
of  any  soil  is  dependent,  to  a  great  extent,  upon  the 
amount  and  form  of  its  nitrogen.  In  soils  of  the 
highest  degree  of  fertility  there  is  usually  present 
from  0.2  to  0.3  per  cent,  of  total  nitrogen,  equivalent 
to  from  7,000  to  10,000  pounds  per  acre  to  the  depth 
of  one  foot.  Many  soils  of  good  crop-producing  power 
contain  as  low  as  0.12  per  cent.  There  is  usually  two 
or  three  times  more  nitrogen  in  the  surface  soil  than 
in  the  subsoil.  In  sandy  soils  which  have  been 
allowed  to  decline  in  fertility,  there  may  be  less  than 
0.04  per  cent.  Of  the  total  nitrogen  in  soils  there  is 
rarely  more  than  2  per  cent,  at  any  one  time,  in  forms 


108  SOILS   AND   FERTILIZERS 

available  as  plant  food.44  A  soil  with  5,000  pounds 
of  total  nitrogen  per  acre  would  contain  about  100 
pounds  of  available  nitrogen,  of  which  only  a  part 
comes  in  contact  with  the  roots  of  crops.  Hence,  it 
is  that  a  soil  may  contain  a  large  amount  of  total 
nitrogen,  and  yet  be  deficient  in  available  nitrogen. 

128.  Amount  of  Nitrogen  Removed  in  Crops. — 
The  amount  of  nitrogen  removed  in  crops  ranges  from 
25  to  100  pounds  per  acre  depending  upon  the  nature 
of  the  crop.  It  does  not  necessarily  follow  that  the 
crop  which  removes  the  largest  amount  of  nitrogen 
leaves  the  land  in  the  most  impoverished  condition. 
Wheat  and  other  grains,  while  they  do  not  remove 
such  a  large  amount  of  nitrogen  in  the  crop,  leave  the 
soil  more  exhausted  than  if  other  crops  were  grown. 
This,  as  will  be  explained,  is  caused  by  the  loss  of 
nitrogen  from  the  soil  in  other  ways  than  through 
the  crop.38 

Pounds  of  nitrogen 
per  acre. 

Wheat,  20  bushels 25 

Straw,  2,000  pounds 10 

Total 35 

Barley,  40  bushels 28 

Straw,  3,000  pounds 12 

Total 40 

Oats,  50  bushels 35 

Straw,  3,000  pounds 15 

Total 50 

Flax,  15  bushels 39 

Straw,    i  ,800  pounds 15 

Total 54 

Potatoes,  150  bushels 40 

Corn,  65  bushels 40 

Stalks,  3,000  pounds 35 

Total 75 


NITROGEN   COMPOUNDS   OF  THE   SOIL  1 09 

129.  Nitrates  and  Nitrites. — The  amount  of  nitro- 
gen in  the  form  of  nitrates  and  nitrites,  varies  from 
mere  traces  to  150  pounds  per  acre.     Calcium  nitrate 
is  the  usual  form  met  with,  especially  in  soils  which 
are  sufficiently  supplied  with  calcium  carbonate  to 
allow  nitrification  to  progress  rapidly.     Nitrates  and 
nitrites  are  the  most  valuable  forms  of  nitrogen  for 
plant   food.     Both    are   produced    from    the   organic 
nitrogen  of  the  soil.     A  nitrate  is  a  compound  com- 
posed of  a  base  element  as  sodium,  potassium,  or  cal- 
cium, combined  with  nitrogen  and  oxygen.     A  nitrite 
contains  less  oxygen  than  a  nitrate. 

Potassium  nitrate,  KNO3>  sodium  nitrate,  NaNO3, 
and  calcium  nitrate,  Ca(NO3)2,  are  the  nitrates  which 
are  of  most  importance  in  agriculture.  The  nitrites, 
as  potassium  nitrite,  KNO2,  are  present  to  a  less 
extent  than  the  nitrates.  Nitrates  and  nitrites  are 
found  in  surface  well  waters  contaminated  with 
animal  and  vegetable  matter.  Many  well  waters 
possess  some  material  value  as  a  fertilizer  on  account 
of  the  nitrates,  nitrites,  and  decaying  animal  and 
vegetable  matters  which  they  contain. 

130.  Ammonium  Compounds   of  the  Soil.  —  The 

amount  of  ammonium  compounds  in  a  soil  is  usually 
less  than  the  amount  of  nitrates  and  nitrites.  The 
sources  of  the  ammonium  compounds  are,  rain-water 
and  the  organic  matter  of  the  soil.  The  ammonium 
compounds  are  all  soluble  and  readily  undergo  fixa- 
tion. See  Section  207.  They  cannot  accumulate  in 
arable  soils,  because  of  nitrification.  They  are  usually 


110  SOILS   AND   FERTILIZERS 

found  in  surface  well  waters.  In  the  soil,  the 
ammonium  compounds  may  be  oxidized  and  form 
nitrates.  Compounds,  as  ammonium  chloride  or  am- 
monium carbonate,  if  present  in  a  soil  in  excessive 
amounts,  will  destroy  vegetation  in  a  way  similar  to 
the  alkaline  compounds  in  alkaline  soils. 

131.  Nitrogen  in   Rain- Water  and  Snow. — The 

amount  of  nitrogen  which  is  annually  returned  to  the 
soil  in  the  form  of  ammonium  compounds  dissolved 
in  rain-water  and  snow,  is  equivalent  to  from  2  to  3 
pounds  per  acre.  At  the  Rothamsted  experiment 
station  the  average  amount  for  eight  years  was  3.37 
pounds.44  When  a  soil  is  rich  in  nitrogen  the  gain 
from  rain  and  snow  is  only  a  partial  restoration  of 
that  which  has  been  given  off  from  the  soil  to  the  air 
or  lost  in  the  drain  waters.  The  principal  form  of 
the  nitrogen  in  rain  water  is  ammonium  carbonate 
which  is  present  in  the  air  to  the  extent  of  about  22 
parts  per  million  parts  of  air. 

132.  Ratio  of  Nitrogen  to  Carbon  in  the  Organic 
Matter  of  Soils. — In  some  soils  the  organic  matter  is 
more  nitrogenous  than  in  others.     In   those  of  the 
arid  regions  the  humus  contains  from  15  to  20  per 
cent,  of  nitrogen,  while  soils  from  the  humid  regions 
contain  4  to  6  per  cent.45     In  some  soils  the  ratio  of 
nitrogen  to  carbon  may  be  i  to  6,  while  in  others  it 
may  be   i   to   18,   or  more.     That  is,  in  the  organic 
matter  of  some  soils  there  is  i  part  of  nitrogen  to  6 
parts  of  carbon,    while  in  others  the  organic  matter 
contains  i  part  of  nitrogen  to  18  parts  of  carbon.     In 


NITROGEN    COMPOUNDS    OF    THE   SOIL  III 

a  soil  where  there  exists  a  wide  ratio  between  the 
nitrogen  and  carbon,  it  is  believed  that  the  conditions 
for  supplying  crops  with  available  nitrogen  are  un- 
favorable. 

133.  Losses  of  Nitrogen  from  Soils. — When  a  soil 
rich  in  nitrogen  is  cultivated  for  a  number  of  years 
exclusively  to  grain  crops  there  is  a  loss  of  nitrogen 
exceeding  the  amount  removed  in  the  crop,  caused  by 
the  rapid  oxidation  of  the  organic  matter  of  the  soil. 
Experiments  have  shown  that  when  a  soil  of  average 
fertility   is  cultivated  continually  to  grain,  for  every 
25    pounds   of   nitrogen  removed   in  the  crop  there 
is  a  loss  of  146  -pounds  from  the  soil  due  to  the  de- 
struction   of  the  organic  matter.18     In  general,    any 
system  of  cropping  which  keeps  the  soil  continually 
under  the  plow,   results  in  decreasing  the   nitrogen. 
When   a  soil  is  rich  in  nitrogen  the  greatest  losses 
occur ;  when  poor  in  nitrogen  there  is  relatively  less 
loss.      When  a  soil  rich  in  nitrogen  is  given  arable 
culture  the  oxidation   of  the  organic  matter  and  the 
losses  of  nitrogen  take  place  rapidly.     The  longer  a 
soil    is   cultivated,  the   slower   the  oxidation  of   the 
humus  and  the  relative  loss  of  nitrogen. 

134.  Gain  of  Nitrogen  in  Soils. — When  arable  land 
is  permanently    covered  with  vegetation,    there  is  a 
gain  of  nitrogen.     Pasture  land  contains  more  nitro- 
gen than  cultivated  land  of  a  similar  character ;  also 
in  meadow  land,  there  is  a  tendency  for  the  nitrogen 
to  increase.     These  facts  are  well   illustrated  in  the 
investigations  of  Lawes  and  Gilbert,  at  Rothamsted.44 


112  SOILS   AND    FERTILIZERS 

Age  of  Pasture  Nitrogen 

Years.  Per  Cent. 

Arable  land o.  14 

Barn-field  pasture 8  0.151 

Apple-tree  pasture 18  0.174 

Meadow 21  0.204 

Meadow 30  0.241 

After  deducting  the  amount  of  nitrogen  in  the  manure 
added  to  the  meadow  land,  the  annual  gain  of  nitrogen 
was  more  than  44  pounds  per  acre. 

Another  source  of  gain  of  nitrogen  is  the  fixation  of 
the  free  nitrogen  of  the  air  by  the  growth  of  clover 
and  other  leguminous  crops.  If  a  soil  is  properly 
manured  and  cropped  the  amount  of  nitrogen  may  be 
increased.  A  rotation  of  wheat,  clover,  wheat,  oats,  and 
corn  with  manure  will  leave  the  soil  at  the  end  of  the 
period  of  rotation  in  better  condition  as  regards  nitro- 
gen than  at  the  beginning.  These  facts  are  illustrated 
in  the  following  table  : l8 

CONTINUOUS  WHEAT  CULTURE — 

Nitrogen  in  soil  at  beginning  of  experiment 0.221  per  cent. 

Nitrogen  at  end  of  5  years  continuous  wheat  culti- 
vation   0.193    "       " 

Loss  per  annum  per  acre  (in  crop  24.5,  soil  146.5).       171  pounds. 

ROTATION  OF  CROPS — 

Nitrogen  in  soil  at  beginning  of  rotation 0.221  per  cent. 

Nitrogen  at  close  of  rotation 0.231    ' 

Gain  to  soil  per  annum  per  acre 61  pounds. 

Nitrogen  removed  in  crops  per  annum 44 

It  is  to  be  regretted  that  in  the  cultivation  of  large 
areas  of  land  to  staple  crops  as  wheat,  corn,  and  cotton, 
the  methods  of  cultivation  followed  are  such  as  to  de- 
crease the  nitrogen  content  and  crop  producing  power 
of  the  soil  when  this  could  be  prevented. 


NITRIFICATION 

135.  Former  Views  Regarding  Nitrification. — The 

presence  of  nitrates  and  nitrites  in  soils  was  formerly 
accounted  for  by  oxidation.  The  theory  was  held 
that  the  production  of  nascent  nitrogen  by  the  de- 
composition of  organic  matter  caused  a  union  be- 
tween the  oxygen  of  the  air  and  the  nitrogen  of  the 
organic  matter.  Fermentation  studies  by  Pasteur  led 
him  to  believe  that  possibly  the  formation  of  nitric 
acid  in  the  soil  might  be  due  to  fermentation.  It  was, 
however,  15  years  later  before  the  French  chemists, 
Schlosing  and  Miintz,  established  the  fact  that  nitrifi- 
cation is  produced  by  a  living  organism. 

136.  Nitrification  Caused  by  Micro-organisms. — 
Nitrification   is   the    process    by   which    nitrates    or 
nitrites  are  produced  in  soils,  by  the  workings  of  or- 
ganisms.    Nitrification  results  in  changing  the   com- 
plex  organic   nitrogen    of   the    soil    to    the   form  of 
nitrates  or  nitrites.     It   is-  the  process  by   which  the 
inert  nitrogen  of  the  soil  is  rendered  available  as  crop 
food.     The  organisms  which  carry  on  the  work  of 
nitrification  have  been  isolated  and  studied  by  War- 
ington,  and  by  Winogradsky. 

137.  Conditions  Necessary  for  Nitrification  are  : 

1.  Food  for  the  nitrifying  organisms. 

2.  A  supply  of  oxygen. 

3.  Moisture. 

4.  A  favorable  temperature. 

5.  Absence  of  strong  sunlight. 

6.  The  presence  of  some  basic  compound. 

(8) 


114  SOILS   AND    FERTILIZERS 

In  order  to  allow  nitrification  to  proceed,  all  of  these 
conditions  must  be  satisfied.  The  process  is  fre- 
quently checked  because  some  of  the  conditions,  as 
presence  of  a  basic  compound,  are  unfulfilled. 

138.  Food  for  the  Nitrifying  Organisms. — All  liv- 
ing organisms  require  food,  and  one  of  the  food  re- 
quirements of  the  nitrifying  organism  is  a  supply  of 
phosphates.  In  the  absence  of  phosphoric  acid, 
nitrification  cannot  take  place.  The  change  which 
the  phosphoric  acid  undergoes  in  serving  as  food  for 
the  nitrifying  organism  is  unknown,  but  it  doubtless 
makes  the  phosphoric  acid  more  available  as  plant 
food91.  The  principal  organic  food  of  the  nitrifying 
organism  is  the  organic  matter  of  the  soil.  Organic 
matter,  only  when  incorporated  with  soil,  can  serve  as 
food  for  the  nitrifying  organism.  In  the  presence  of 
a  large  amount  of  organic  matter,  as  in  a  manure 
pile,  nitrification  does  not  take  place.  The  process 
can  take  place  only  when  the  organic  matter  is  largely 
diluted  with  soil.  Under  favorable  conditions  nitrify- 
ing organisms  may  take  all  of  their  food  in  inorganic 
forms  ;  that  is,  nitrification  may  take  place  in  the  ab- 
sence of  organic  matter  provided  the  proper  mineral 
food  be  supplied.  When  growth  under  such  condi- 
tions takes  place  the  organisms  assimilate  carbon 
from  the  combined  carbon  of  the  air,  and  produce 
organic  carbon  compounds.  An  organism,  working 
in  the  absence  of  sunlight  and  unprovided  with 
chlorophyl,  may  construct  organic  carbon  com- 
pounds.44 The  nitrification  which  takes  place  in  the 
absence  of  nitrogeneous  organic  matter  is  of  too 


NITRIFICATION  115 

limited  a  character  to  supply  growing  crops  with  all 
of  their  available  nitrogen.  For  general  crop  pro- 
duction the  organic  matter  of  the  soil  is  the  source  of 
the  nitrogen  which  undergoes  the  nitrification  process, 
and  which  furnishes  food  for  the  nitrifying  organisms. 

139.  Oxygen  Necessary  for    Nitrification.  —  The 
second   requirement   for   nitrification  is  an  adequate 
supply  of  oxygen.    The  nitrification  organism  belongs 
to  that  class  of  ferments  (aerobic)  which  requires  oxy- 
gen for  existence.     Oxygen  is  present  as  one  of  the 
elements  in  the  final  product  of  nitrification  as  in  cal- 
cium  nitrate,  Ca(NO  )a.     In  the  absence  of  oxygen 
the  nitrification  process  is  checked.     When  soils  are 
saturated  with  water,  the  process  cannot  go  on  for 
want   of   oxygen.     Cultivation,    particularly   of  clay 
soils,    favors    nitrification   increasing   the   supply    of 
oxygen  in  the  soil. 

140.  Moisture  Necessary  for  Nitrification. — Nitri- 
fication cannot  take  place  in  a  soil  deficient  in  mois- 
ture.    As  in  all  fermentation  processes,  so  with  nitri- 
fication, moisture  is  necessary  for  the  chemical  changes 
to  take  place.     In  a  very  dry  time  nitrification   is  ar- 
rested for  want  of  water.     Water  is    as  necessary   to 
the  growth  and  development  of  the  living  organism 
which  carries  on  the  work  of  nitrification,  as  it  is  to 
the  life  of  a  plant  of  higher  order. 

141.  Temperatures  Favorable  for  Nitrification. — 
The  most  favorable  temperatures  for  nitrification  are 
between  12°  C.  (54°  F.)  and  37°  C.  (99°  F.).     It  may 


Il6  SOILS   AND   FERTILIZERS 

take  place  at  as  low  a  temperature  as  3°  or  4°  C. 
(37°  and  39°  F.);  at  50°  C.  (122°  F.)  it  is  feeble, 
while  at  55°  C.  (130°  F.)  there  is  no  action.44.  In 
northern  latitudes  nitrification  is  checked  during  the 
winter,  while  in  southern  latitudes  this  change  takes 
place  during  the  entire  year.  As  a  result  many  soils 
in  southern  latitudes  contain  less  nitrogen  than  soils 
in  northern  latitudes  where  fermentation  and  leaching 
of  nitrates  is  checked  by  climatic  conditions.  Crops 
which  require  their  nitrogen  early  in  the  growing 
season  are  frequently  placed  at  a  disadvantage  be- 
cause there  is  less  available  nitrogen  in  the  soil  at 
that  time  than  later. 

142.  Strong  Sunlight  Checks  Nitrification. — Nitri- 
fication cannot  take  place  in  strong  sunlight ;  it  pre- 
vents the   action  of  all   organisms  of  this  class.     In 
fallow  land  there  is  no  nitrification  at  the  surface  but 
immediately  below  where  the  sunlight  is  excluded  by 
the  surface  soil,  it  is  most  active.     In  a  cornfield  it  is 
more  active  than  in  a  compacted  fallow  field. 

143.  Base-forming  Elements  Essential  for  Nitrifi- 
cation.— The  presence  of  some  base-forming  element 
to  combine  with  the  nitric  acid  produced  is  a  neces- 
sary condition  for  nitrification,  and  for  this  purpose 
calcium  carbonate  is  particularly  valuable.     The  ab- 
sence of  basic  materials  is  one  of  the  frequent  causes 
of    non-nitrification.     In  acid    soils,    the    process    is 
checked  for  the  want  of  proper  basic  material.     The 
organisms  which  carry  on  the  work  cannot  exist  in 
strong  acid  or  alkaline  solution,  consequently  in  such 
soils  nitrification  cannot  take  place.17 


NITRIFICATION  1 17 

144.  Nitrous  Acid  Organisms.  —  There  are  at  least 
two  nitrifying  organisms  in  the  soil ;  one  produces 
nitrates  and  the  other  nitrites  or  nitrous  acid.     It  is 
believed  that  the  process  takes  place  in  two  stages, 
the  first  being  performed   by  the  nitrous  organism, 
and  the  process  being  completed  by  the  nitric  organ, 
ism.     Warington    says    that    "  both    organisms    are 
present  in  the  soil  in  enormous  numbers,  —  and  the 
action  of  the  two  organisms  proceeds  together,  as  the 
conditions  are  favorable  to  both." 

145.  Ammonia-producing   Organisms.  —  There  are 
also  present  in  the  soil   organisms  which  have  the 
power  of  producing  ammonia   from    proteid  bodies. 
The  ammonium  compounds  produced  are  acted  upon 
by  the  nitrifying  organisms  and  readily  undergo  nitri- 
fication.46 

146.  Denitrification  is  just  the  reverse  of  the  nitri- 
fication process,  and  is  the  result  of  the  workings  of  a 
class  of  organisms  which  feed  upon  the  nitrates  form- 
ing free  nitrogen  which  is  liberated  as  a  gas.     One  of 
the  conditions  for  denitrification  is  absence  of  air,  as 
the  organisms  belong  to  the  anaerobic  class.     Denitri- 
fication readily  takes   place   in   soils   saturated  with 
water,  and  where  the  soil  is  compacted  so  that  air  is 
practically  excluded.47 

147.  Number  and  Kinds  of  Organisms  in  Soils.  — 
In  addition  to  the  micro-organisms  which  carry  on  the 
work  of  nitrification,  denitrification,  and  ammonifica- 
tion,  there  are  a  great  many  others,  some  of  which  are 


Il8  SOILS   AND   FERTILIZERS 

beneficial  while  others  are  injurious  to  crop  growth. 
It  has  been  estimated  that  in  a  gram  of  an  average 
sample  of  soil  there  are  from  60,000  to  500,000  bene- 
ficial and  injurious  micro-organisms.48  There  are  pro- 
duced from  many  crop  residues,  by  injurious  ferments, 
chemical  products  which  may  be  destructive  to  crop 
growth.  Flax  straw,  for  example,  when  it  decays  in 
the  soil  forms  chemical  products  which  are  destructive 
to  a  succeeding  flax  crop. 

A  moist  soil,  rich  in  organic  matter,  and  containing 
various  salts,  may  form  the  medium  for  the  propaga- 
tion of  all  classes  of  organisms.  Sewage-sick  soils 
clover-sick  soils,  and  flax-diseased  lands  are  all  the  re- 
sults of  bacterial  diseases.  Many  of  the  organisms 
which  are  the  cause  of  such  diseases  as  typhoid  fever, 
and  cholera,  may  propagate  and  develop  in  a  moist 
soil  under  certain  conditions,  and  then  find  their 
way  through  drain  water  into  surface  wells,  and  cause 
these  diseases  to  spread. 

148.  Products  Formed  by  Soil  Organisms.  —  In 
considering  the  part  which  micro-organisms  take  in 
plant  growth,  as  well  as  in  all  similar  processes,  there 
are  two  phases  to  be  considered:  (i)  the  action  of  the 
organism  itself,  and  (2)  the  chemical  action  of  the  pro- 
duct of  the  organism.  In  the  case  of  nitrification,  the 
action  of  the  organism  brings  about  a  change  in  the 
composition  of  the  organic  matter,  producing  nitric 
acid  which  is  merely  a  product  formed  as  a  result  of 
the  action  of  the  organism.  The  nitric  acid  then  acts 
upon  the  soil,  producing  nitrates.  In  the  case  of  soils 
rich  in  organic  matter,  the  fermentation  changes  which 


n9 

take  place  during  humification  result  in  the  produc- 
tion of  acid  products.  This  is  simply  the  result  of 
the  action  of  the  ferments.  The  acids  then  act  upon 
the  soil  bases  and  produce  humates  or  organic  salts. 
In  many  fermentation  changes  there  is  first  the  pro- 
duction of  some  chemical  compound,  and  then  the 
action  of  this  compound  upon  other  bodies.  In  ren- 
dering plant  food  available,  as  in  nitrification  and 
humification,  it  is  the  final  product,  and  not  the  first 
product  of  the  organism,  which  is  of  value. 

149.  Inocculating  Soils  with  Organisms. — In  grow- 
ing leguminous  crops  on  soils  where  they  have  never 
before  been  produced,  it  has  been  proposed  to  supply 
the  essential  organisms  which  assist  the  crops  to  ob- 
tain their  nitrogen.     For  example,  if  clover  is  grown 
on  new  land,  the  soil  is  liable  to  be  deficient  in  the 
organisms  which  assist  in  the  assimilation  of  nitrogen 
and    which    are   present   in  the  root  nodules  of  the 
plant.     If  these  organisms  are  supplied,  better  condi- 
tions for  growth  exist.     Some  soils  are  benefitted  by 
inocculation,    while   others   are  not.     The  extent  to 
which  it  is  necessary  to  inocculate  different  soils  with 
organisms  for  the  assimilation  of  nitrogen,  has  not  yet 
been  determined  by  actual  field  experiments. 

150.  Loss  of  Nitrogen  by  Fallowing  Rich  Lands. — 

Summer  fallowing  creates  conditions  favorable  to 
nitrification.  A  fallow  is  beneficial  to  a  succeeding 
crop  because  of  the  nitrogen  which  is  rendered  avail- 
able. If  a  soil  is  rich  in  nitrogen  and  lime,  summer 
fallowing  causes  the  production  of  more  nitrates  than 


120  SOILS   AND    FERTILIZERS 

can  be  retained  in  the  soil.  The  crop  utilizes  only  a 
part  of  the  nitrogen  rendered  available,  the  rest  being 
lost  by  drainage,  ammonincation,  and  denitrification. 
Hence  the  available  nitrogen  is  increased  while  the 
total  nitrogen  is  greatly  decreased.17 

Soil  before  Soil  after 

fallowing.  fallowing. 

Total  nitrogen 0.154  0.142 

Soluble  nitrogen 0.002  0.004 

The  gain  of  0.002  per  cent,  of  soluble  nitrogen  was 
accompanied  by  a  loss  of  0.012  per  cent,  of  total 
nitrogen.  For  every  pound  of  available  nitrogen 
there  was  a  loss  of  six  pounds.  Bare  fallowing  of 
land  should  not  be  practiced,  except  occasionally  to 
destroy  weeds  or  insects,  as  it  results  in  permanent 
injury  to  the  soil. 

151.  Influence  of  Plowing  upon  Nitrification.  — 
In  a  rich  prairie  soil  nitrification  goes  on  very  rapidly. 
This  is  one  reason  why  shallow  plowing  on  new 
breaking  gives  better  results  than  deep  plowing. 
Deep  plowing  at  first,  causes  nitrification  to  take  place 
to  such  an  extent  that  the  crop  is  overstimulated  in 
growth,  due  to  an  excess  of  available  nitrogen.  Deep 
plowing  and  thorough  cultivation  aid  nitrification. 
The  longer  a  soil  has  been  cultivated,  the  deeper  and 
more  thorough  must  be  the  cultivation. 

Early  fall  plowing  leaves  more  available  nitrogen 
at  the  disposal  of  the  crop  than  late  fall  plowing. 
Nitrification  takes  place  only  near  the  surface.  Hence 
when  late  spring  plowing  is  practiced  there  is  brought 
to  the  surface  raw  nitrogen,  while  the  available  nitro- 


NITROGENOUS   MANURES  121 

gen  has  been  plowed  under,  and  is  beyond  the  reach 
of  the  young  plants  when  they  require  the  most  help 
in  obtaining  food.  The  various  methods  of  cultiva- 
tion as  deep  and  shallow  plowing,  spring  and  fall 
plowing,  and  surface  cultivation  have  as  much  influ- 
ence upon  the  available  nitrogen  supply  of  crops  as 
upon  the  water  supply.  The  saying  that  cultivation 
makes  plant  food  available  is  particularly  true  of  the 
element  nitrogen,  the  supply  of  which  is  capable  of 
being  increased  or  decreased  to  a  greater  extent  than 
that  of  any  other  element. 

NITROGENOUS  MANURES 

152.  Sources  of  Nitrogenous  Manures.  —  The  mate- 
rials used  for  enriching  soils  with  nitrogen,  to  promote 
crop  growth,  may  be  divided  into  two  classes  :  (i) 
organic  nitrogenous  manures,  (2)  mineral  nitrogenous 
manures.  Each  of  these  classes  has  a  different  value 
as  plant  food,  and  in  fact  there  are  marked  differences 
in  fertilizer  value  between  materials  belonging  to  the 
same  class.  The  nitrogenous  organic  materials  used 
for  fertilizing  purposes  are ;  dried  blood,  tankage, 
meat  scraps  and  flesh  meal,  fish  offal,  cottonseed  meal, 
and  leguminous  crops  as  clover  and  peas.  The  nitro- 
gen in  these  substances  is  principally  in  the  form  of 
protein.  When  peat  and  muck  are  properly  used 
they  also  may  be  classed  among  the  nitrogenous 
manures.  The  mineral  nitrogenous  manures  are 
nitrates,  as  sodium  nitrate,  and  ammonium  salts,  as 
ammonium  sulphate. 

123.  Dried   Blood. — This   is  obtained   by  drying 


122  SOILS   AND   FERTILIZERS 

the  blood  and  debris  from  slaughter-houses.  Fre- 
quently small  amounts  of  salt  and  slaked  lime  are 
mixed  with  the  blood.  It  is  richest  in  nitrogen  of 
any  of  the  organic  manures.  When  thoroughly  dry 
it  may  contain  14  per  cent,  of  nitrogen.  As  usually 
sold,  it  contains  from  10  to  20  per  cent,  of  water,  and 
has  a  nitrogen  content  of  from  9  to  13.  Dried  blood 
contains  only  small  amounts  of  other  fertilizer  ele- 
ments ;  it  is  strictly  a  nitrogenous  fertilizer,  readily 
yielding  to  the  action  of  micro-organisms  and  to  nitri- 
fication. On  account  of  its  fermentable  nature,  it  is 
a  quick-acting  fertilizer,  and  is  one  of  the  most  valu- 
able of  the  organic  materials  used  as  manure.  It 
gives  the  best  returns  when  used  on  an  impoverished 
soil  to  aid  crops  in  the  early  stages  of  growth,  before 
the  inert  nitrogen  of  the  soil  becomes  available. 
Dried  blood  may  be  applied  as  a  top  dressing  on  grass 
land,  and  it  is  also  an  excellent  form  of  fertilizer  to 
use  on  many  garden  crops,  but  it  should  not  be  placed 
in  direct  contact  with  seeds,  as  it  will  cause  rotting, 
nor  should  it  be  used  in  too  large  amounts.  Three 
hundred  pounds  per  acre  is  as  much  as  should  be  ap- 
plied at  one  time.  When  too  much  is  used  losses  of 
nitrogen  may  occur  by  leaching  and  by  denitrification. 
It  is  best  applied  directly  to  the  soil,  as  a  top  dressing 
in  the  case  of  grass,  or  near  the  seeds  of  garden  crops, 
and  not  mixed  with  unslaked  lime  or  wood  ashes,  but 
each  should  be  used  separately.  As  all  plants  take  up 
their  nitrogen  early  in  their  growth,  nitrogenous  fer- 
tilizers as  blood  should  be  applied  before  seeding  or 
soon  after.  An  application  of  dried  blood  to  partially 


NITROGENOUS   MANURES  123 

matured  garden  crops  will  cause  a  prolonged  growth 
and  very  late  maturity. 

Storer  gives  the  following  directions  for  preserving 
any  dried  blood  produced  upon  farms.22  "  The  blood 
is  thoroughly  mixed  in  a  shallow  box  with  4  or  5 
times  its  weight  of  slaked  lime.  The  mixture  is  cov- 
ered with  a  thin  layer  of  lime  and  left  to  dry  out.  It 
will  keep  if  stored  in  a  cool  place,  and  may  be  applied 
directly  to  the  land  or  added  to  a  compost  heap." 

The  price  per  pound  of  nitrogen  in  the  form  of 
dried  blood  can  be  determined  from  the  cost  and  the 
analysis  of  the  material.  A  sample  containing  9  per 
cent,  of  nitrogen  and  selling  for  $28  per  ton  is  equiva- 
lent to  15.55  cents  Per  pound  for  the  nitrogen  (2000  X 
0.09  —  180.  $28.00  -*r  180  =  15.55  cents). 

154.  Tankage  is  composed.of  refuse  matter  as  bones, 
trimmings  of  hides,  hair,  horns,  hoofs  and  some  blood. 
The  fat  and  gelatin  are,  as  a  rule,  first  removed  by 
subjecting  the  material  to  superheated  steam.  This 
miscellaneous  refuse,  after  drying,  is  ground  and 
sometimes  mixed  with  a  little  slaked  lime  to  prevent 
rapid  fermentation. 

Tankage  contains  less  nitrogen  but  more  phosphoric 
acid  than  dried  blood.  Owing  to  its  miscellaneous 
nature,  it  is  quite  variable  in  composition,  as  the  fol- 
lowing analyses  of  tankage  from  the  same  abattoir  at 
different  times  show.14 

First  year.  Second  year.  Third  year. 

Moisture 10.5  9.8  10.9 

Nitrogen 5.7  7.6  6.4 

Phosphoric  acid 12.2  10.6  11.7 


124  SOILS   AND    FERTILIZERS 

As  a  general  rule,  tankage  contains  from  5  to  8  per 
cent,  of  nitrogen  and  from  6  to  14  per  cent,  of  phos- 
phoric acid.  It  is  much  slower  in  its  action  than 
dried  blood,  and  supplies  the  crop  with  both  nitrogen 
and  phosphoric  acid.  Tankage  is  a  valuable  form  of 
ferlizer  to  use  for  garden  purposes.  It  may  also  be 
used  as  a  top  dressing  on  grass  lands,  and  may  be 
spread  broadcast  on  grain  lands.  It  is  best  to  apply 
the  tankage,  when  possible,  a  few  days  prior  to  seed- 
ing, and  it  should  not  come  in  contact  with  seeds. 
Two  hundred  and  fifty  pounds  per  acre  is  a  safe  dress- 
ing, and  when  there  is  sufficient  rain  to  ferment  the 
tankage,  400  pounds  per  acre  may  be  used.  A  dressing 
of  800  pounds  in  a  dry  season  would  be  destructive  to 
vegetation.  On  impoverished  soil  more  may  be  used 
than  on  soils  which  are  for  various  reasons  out  of 
condition.  The  cost  of  the  nitrogen,  as  tankage,  may 
be  determined  from  the  composition  and  selling  price. 
If  tankage  containing  7  per  cent,  of  nitrogen  and  12 
per  cent,  of  phosphoric  acid  is  selling  for  $32  per  ton, 
what  is  the  cost  of  the  nitrogen  per  pound  ?  The 
market  value  of  phosphoric  acid,  in  the  form  of  bones, 
should  first  be  ascertained.  Suppose  that  bone  phos- 
phoric acid  is  selling  for  4  cents  per  pound.  The 
phosphoric  acid  in  the  ton  of  tankage  would  then  be 
worth  $9.60,  making  the  nitrogen  cost  $22.40.  The 
140  pounds  of  nitrogen  in  the  ton  of  fertilizer  would 
be  worth  $22.40,  or  16  cents  per  pound.  In  eastern 
markets  the  price  of  tankage  is  usually  much  higher 
than  near  the  large  packing  houses  of  the  west. 

155,  Flesh  Meal.  —  The  flesh  refuse  from  slaugh- 


NITROGENOUS   MANURES  125 

ter-houses  is  sometimes  kept  separate  from  the  tank- 
age and  sold  as  flesh  meal,  the  fat  and  gelatin  being 
first  removed  and  used  for  the  manufacture  of  glue  and 
soap.  Flesh  meal  is  variable  in  composition  and  may 
be  very  slow  in  decomposing.  It  contains  from  4  to 
8  per  cent,  or  more  of  nitrogen  with  an  appreciable 
amount  of  phosphoric  acid.  Occasionally  it  is  used 
for  feeding  poultry  and  hogs,  and  cattle  to  a  limited 
extent.  When  thus  used  the  fertilizer  value  of  the 
dung  is  nearly  equivalent  to  the  original  value  of  the 
meal. 

156.  Fish  Scrap.  —  The  flesh  of  fish  is  very  rich  in 
nitrogen.49    The  offal  parts,  as  heads,  fins,  tails  and  in- 
testines, are  dried  and  prepared  as  a  fertilizer.     Some 
species  of  fish  which  are  not  edible  are  caught  in  large 
numbers  to  be  used  for  this  purpose.      In   sea-coast 
regions  fish  fertilizer  is  one  of  the  cheapest  and  best  of 
the  nitrogenous  manures.     It  is   richer  in  nitrogen 
than  tankage  or  flesh  meal,  and  in  many  cases  equal 
to  dried  blood.     It  readily  undergoes  nitrification  and 
is  a  quick-acting  fertilizer. 

157.  Seed  Residues.  —  Many  seeds,   as  cottonseed 
and  flaxseed,  are  exceeding  rich  in  nitrogen.     When 
the  oil  has  been  removed,  the  flaxseed  and  cottonseed 
cake  are  proportionally  richer  in  nitrogen  than  the 
original   seed.     This  cake  is    usually  sold  as  cattle 
food,  but  occasionally  is  used  as  fertilizer.      Cotton- 
seed cake  contains  from  6  to  7  per    cent,  of    nitro- 
gen, and  compares  fairly  well  in  nitrogen  content  with 
animal  bodies.     Cottonseed  cake  and  meal  are  not  so 
quick-acting  as  dried  blood,  but  when  used  in  south- 


126  SOILS   AND   FERTILIZERS 

ern  latitudes  a  little  time  before  seeding,  the  nitrogen 
becomes  available  for  crop  purposes.  Oil  meals,  as 
cottonseed  and  linseed,  containing  a  high  per  cent,  of 
oil  are  much  slower  in  decomposing  than  those  which 
contain  but  little  oil.  It  is  better  economy  to  feed  the 
cake  to  stock  and  use  the  manure  than  to  apply  the 
cake  directly  to  the  land.  Occasionally  however 
cottonseed  meal  has  been  so  low  in  price  that  its  use 
as  a  fertilizer  has  been  admissible. 

A  ton  of  cottonseed  meal  costing  $20  and  containing 
2  per  cent,  of  phosphoric  acid  and  7  per.  cent  of 
nitrogen  would  be  equivalent  to  13.1  cents  per  pound 
for  the  nitrogen,  which  is  frequently  cheaper  than 
purchasing  some  other  nitrogenous  fertilizer. 

158.  Leather,  Wool  Waste  and  Hair  are  rich  in 
nitrogen,  but  on  account  of  their  slow  rate  of  decom- 
posing are  unsuitable  for  fertilizer  purposes.  When 
present  in  fertilizers  they  give  poor  field  results. 

One  of  the  methods  employed  to  detect,  in  fertili- 
zers, the  presence  of  inert  forms  of  nitrogen  as  leather, 
is  to  digest  the  material  in  prepared  pepsin  solution.50 
Substances  like  dried  blood  are  nearly  all  soluble  in 
the  pepsin,  while  leather  and  other  inert  forms  are 
only  partially  so.  The  solubility  of  the  organic  nitro- 
gen in  pepsin  solution  determines,  to  a  great  extent, 
the  value  of  the  material  as  a  fertilizer.51 

Soluble  in  prepared 

pepsin  solution 
Per  cent,  of  nitrogen. 

Dried  blood 94. 2 

Ground  dried  fish 75.7 

Tankage 73.6 

Cottons  eed  meal 86.4 

Hoofand  horn  meal 30.0 

Leather 16.7 


NITROGENOUS   MANURES  1 27 

159.  Peat  and  Muck.—  Many  samples  of  peat  and 
muck  are  quite  rich  in  nitrogen.     The  nitrogen  is, 
however,  in  an  insoluble  form,  and  is  with  difficulty 
nitrified.     When  mixed  with  stable  manure,  particu- 
larly liquid  manure,  with  the  addition  of  a  little  lime 
fermentation  may  be  induced,  and  a  valuable  manure 
produced.     Muck  and  peat  should  be  dried  and  sun- 
cured,  and  then  used  as  absorbents  in  stables.     Peat 
differs  from  muck  in  being  fibrous.     If  the  muck  gives 
an  acid  reaction,  lime  (not  quicklime)  should  be  used 
with  it  in  the  stable,  as  directed  under  farm  manures. 
When  easily  obtained   muck   is  one  of  the  cheapest 
forms  of  nitrogen. 

COMPOSITION  OF  DRY  MUCK  SAMPLES.17 

Nitrogen. 
Per  cent. 

Marshy  place,  producing  hay 2.21 

Marshy  place,  dry  in  late  summer 2.01 

Old  lake  bottom 1.81 

160.  Leguminous  Crops  as  Nitrogenous  Manures. 

— The  frequent  use  of  leguminous  crops  for  manurial 
purposes  is  the  cheapest  way  of  obtaining  nitrogen. 
When  the  crop  is  not  removed  from  the  land  but  is 
plowed  under  while  green,  the  practice  is  called  green 
manuring.  This  does  not  enrich  the  land  with  any 
mineral  material  but  results  in  changing  to  humate 
forms  inert  plant  food.  Green  manuring,  with  le- 
guminous crops,  should  take  the  place  of  bare  fallow, 
as  its  effects  upon  the  soil  are  more  beneficial.  With 
green  manuring,  nitrogen  is  added  to  the  soil  while 
with  bare  fallow  there  is  a  loss  of  nitrogen.  Legu- 
minous crops,  as  clover,  peas,  crimson  clover,  and  cow 
peas,  should  be  made  to  serve  as  the  main  source  of 
the  nitrogen  for  crop  production. 


128  SOILS   AND   FERTILIZERS 

161.  Sodium  Nitrate. — The  nitric  nitrogen  most 
frequently  met  with  in  commercial  forms  is  sodium 
nitrate,  commonly  known  as  Chili  saltpeter.  It  is  a 
natural  deposit  found  extensively  in  Chili,  Peru,  and 
the  United  States  of  Colombia.  Various  theories  have 
been  proposed  to  account  for  these  deposits,  but  it  is 
difficult  to  determine  just  how  they  have  been  formed.10 
Their  value  to  agriculture  may  be  estimated  from  the 
fact  that  there  are  annually  used  in  the  United  States 
about  100,000  tons,  and  in  Europe  about  700,000  tons. 
The  commercial  value  of  nitrogen  in  fertilizers  is  reg- 
ulated by  the  price  of  sodium  nitrate  which,  when 
pure,  contains  16.49  Per  cent-  of  nitrogen.  Commer- 
cial sodium  nitrate  is  from  95  to  97  per  cent.  pure. 
An  ordinary  sample  contains  about  16  per  cent,  of 
nitrogen  and  costs  from  $50  to  $60  per  ton,  making 
the  nitrogen  worth  from  15  to  18  cents  per  pound. 
Sodium  nitrate  is  the  most  active  of  all  the  nitrogenous 
manures.  It  is  soluble  and  does  not  have  to  undergo 
the  nitrification  process  before  being  utilized  by  crops. 
On  account  of  its  extreme  solubility  it  should  be  ap- 
plied sparingly,  for  it  cannot  be  retained  in  the  soil. 
As  a  top  dressing  on  grass,  it  will  respond  by  impart- 
ing a  rich  green  color.  It  may  be  used  at  the  rate  of 
250  pounds  per  acre,  but  a  much  lighter  application 
will  generally  be  found  more  economical.  Sodium 
nitrate  may  contain  traces  of  sodium  perch lorate, 
which  is  destructive  to  vegetation  if  the  fertilizer  is 
used  in  excess.52  Sodium  nitrate,  in  small  amounts, 
is  the  fertilizer  most  frequently  resorted  to  when  the 
forcing  of  crops  is  desired  as  in  early  market  garden- 


NITROGENOUS   MANURES  129 

ing.  Its  use  for  fertilizing  horticultural  crops  has  be- 
come equally  as  extensive  as  for  general  farm  crops. 
Excessive  amounts  may  produce  injurious  results. 
Sodium  nitrate  stimulates  a  rank  growth  of  dark 
green  foliage,  and  retards  the  maturity  of  plants,  "but 
when  properly  used  is  one  of  the  most  valuable  of 
the  nitrogenous  "fertilizers. 

162.  Ammonium  Salts.  — Ammonium   sulphate   is 
obtained  as  a  by-product  in  the  manufacture  of  illumi- 
nating gas  and  is  extensively  sold  as  a  fertilizer.     It 
usually  contains  about  20  per  cent,  of  nitrogen,  equiv- 
alent to  95  per  cent,  of  ammonium  sulphate,  the  re- 
maining 5  per  cent,   being  moisture  and  impurities. 
Ammonium   sulphate  is  not  generally  considered  the 
equivalent  of  sodium  nitrate.     It  is,  however,  a  valua- 
ble form  of  nitrogen.     The  statements  made  regarding 
the  use  of  sodium  nitrate   apply  equally  well  to  the 
use  of  ammonium  sulphate.     Ammonium  chloride  and 
ammonium  carbonate  are  not  suitable  for  fertilizers 
on  account  of  their  destructive  action  upon  vegetation. 

163.  Nitrogen  and  Ammonia  Equivalent  of  Fer- 
tilizers.  —  Nitrogenous    fertilizers    are    sometimes 
represented  as  containing  a  certain  amount  of  ammo- 
nia   instead    of    nitrogen.     Fourteen-seventeenths   of 
ammonia  is  nitrogen,  and  if  a  fertilizer  contains  2.25 
per  cent,  ammonia,  it  is  equivalent  to  1.85  per  cent, 
of  nitrogen.     To   convert  NH   results  to  an  N  basis 
multiply  by  0.823. 

164.  Purchasing  Nitrogenous  Manures.  —  In  pur- 
chasing nitrogenous  manure,   the  special  purpose  for 
which  it  is  to  be   used  should   always   be   considered. 

(9) 


130  SOILS   AND   FERTILIZERS 

Under  some  conditions,  as  forcing  a  crop  on  an  im- 
poverished soil,  sodium  nitrate  is  desirable.  Under 
other  conditions  tankage,  cottonseed  cake,  or  some 
other  form  of  nitrogen  may  be  made  to  answer  the 
purpose.  There  is  annually  expended  in  purchasing 
nitrogenous  fertilizers  a  large  amount  of  money  which 
could  be  expended  more  ecomically,  if  the  science  of 
fertilizing  were  given  a  more  careful  study.  The 
uses  of  nitrogenous  fertilizers  for  special  crops  and 
the  testing  of  soils  to  determine  any  deficiency  in 
nitrogen  are  discussed  in  Chapters  X  and  XI  which 
treat  of  commercial  fertilizers  and  the  food  require 
ments  of  farm  crops. 


CHAPTER  V 

FARM  MANURE 

165.  Variable  Composition  of  Farm  Manures. — 

The  term  farm  manure  does  not  designate  a  prod- 
uct of  definite  composition.  Manure  is  the  most 
variable  in  chemical  composition  of  any  of  the  mate- 
rials produced  on  the  farm.  It  may  contain  a  large 
amount  of  straw,  in  which  case  it  is  called  coarse  ma- 
nure ;  or  it  may  contain  only  the  solid  excrements  and 
a  little  straw,  the  liquid  excrements  being  lost  by 
leaching ;  then  again  it  may  consist  of  the  droppings 
of  poorly  fed  animals,  or  of  the  mixed  excrements  of 
different  classes  of  well-fed  animals. 

The  term  stable  manure  has  been  proposed  for 
that  product  which  contains  all  of  the  solid  and  liquid 
excrements  with  the  necessary  absorbent,  before  any 
losses  have  been  sustained.16  The  term  barnyard 
manure  is  restricted  to  that  material  which  accumu- 
lates around  some  barns  and  farm  yards,  and  is  ex- 
posed to  leaching  rains  and  the  drying  action  of  the 
sun. 

1 66.  Average  Composition  of  Manures. — The  solid 
excrements  of  animals  contain  from  60  to  85  per  cent, 
of  water ;  when  mixed  with  straw,  and  the  liquid  ex- 
crements  are  retained,   the  mixed   manure  contains 
about   75   per  cent,   of  water.     The  nitrogen  varies 
from  0.4  to  0.9  per  cent.,  according  to  the  nature  of 
the  food  and  the  extent  to  which  other  factors  have 


132 


SOILS   AND   FERTILIZERS 


affected  the  composition.     In  general,  animals  consu- 
ming liberal  amounts  of  coarse  fodders  produce  manure 


Fig.  24.     Average  composition  of  Fig.  25.     Manure  after  six 

fresh  manure?  months'  exposure, 

i.  Nitrogen.     2.  Phosphoric  acid. 
3.  Potash.         4.  Mineral  matter. 

with  a  higher  per  cent,  of  potash  than  of  phosphoric 
acid.  This  is  because  the  potash  in  the  food  exceeds 
the  phosphoric  acid.  The  average  composition  of 
mixed  stable  manure  is  as  follows : 


Average 
Per  cent. 


Nitrogen 0.50 

Phosphoric  acid 0.35 

Potash 0.50 


Range 
Per  cent. 

0.4  to  0.8 

0.2  tO  0.5 

0.3  to  0.9 


In  calculating  the  amount  of  fertility  in  manures, 
it  is  more  satisfactory  to  compute  the  value  from  the 
food  consumed  and  the  care  which  the  manure  has 
received,  than  to  use  figures  expressing  average  com- 
position. 

167.  Factors  which  Influence  the  Composition  and 
Value  of  Farm  Manure. — 

I.  Kind  and  amount  of  absorbents  used. 

II.  Kind  and  amount  of  food  consumed. 


FARM  MANURE  133 

III.  Age  and  kind  of  animals. 

IV.  Methods  employed    in  collecting,  preserving 
and  utilizing  the  manure. 

Any  one  of  the  above,  as  well  as  many  minor 
factors,  may  influence  the  composition  and  value  of 
farm  manure. 

168.  Absorbents. — The  most  universal   absorbent 
is  straw.     Wheat  straw  and   barley  straw  have  about 
the  same   manurial  value.     Oat  straw  is  more  valu- 
able.    The  average  composition  of  straw  and  other 
absorbents  is  as  follows  : 

Straw.         I^eaves.          Peat.          Sawdust. 
Per  cent.      Per  cent.      Per  cent.      Per  cent. 

Nitrogen 0.40  0.6  i.o  o.i 

Phosphoric  acid 0.36  0.3  ..  0.2 

Potash 080  0.3  ..  0.4 

When  a  large  amount  of  straw  is  used  the  per  cent, 
of  nitrogen  and  phosphoric  acid  is  decreased,  while  the 
per  cent,  of  potash  is  slightly  increased.  Sawdust 
and  leaves  both  make  the  manure  more  dilute.  Dry 
peat  makes  the  manure  richer  in  nitrogen.  The  ab- 
sorbent powers  of  these  different  materials  are  about 
as  follows : I4 

Per  cent,  of 
water  absorbed. 

Fine  cut  straw 30.0 

Coarse  uncut  straw 18.0 

Peat 60.0 

Sawdust 45.0 

The  proportion  of  absorbents  in  manure  ranges  from 
a  fifth  to  a  third  of  the  total  weight  of  the  manure. 

169.  Use  of  Peat  and  Muck  as  Absorbents. — On 
account  of  the  high  per  cent,  of  nitrogen  in  peat  and 


134  SOILS   AND    FERTILIZERS 

the  power  which  it  possesses  when  dry  of  absorbing 
water,  it  is  a  valuable  material  to  use  as  an  absorbent 
in  stables.  As  previously  explained,  peat  is  slow  of 
decomposition,  but  when  mixed  with  the  liquid  ma- 
nure it  readily  yields  to  fermentation,  particularly  if 
a  little  land  plaster  or  marl  be  used  in  the  stable  along 
with  the  peat.  Peat  has  high  absorptive  power  for 
gases  as  well  as  liquids,  and  when  used  stables  are 
rendered  particularly  free  from  foul  odors. 

RELATION  OF  FOOD  CONSUMED  TO  MANURE  PRODUCED 

170.  Bulky  and  Concentrated  Foods.  —  The  more 
concentrated  and  digestible  the  food  consumed,  the 
more  valuable  is  the  manure.  Coarse  bulky  fodders 
always  give  a  large  amount  of  a  poor  quality  of  ma- 
nure. For  example,  the  manure  from  animals  fed  on 
timothy  hay  and  that  from  animals  fed  on  clover  hay 
and  grain,  show  a  wide  difference  in  composition. 
The  dry  matter  of  timothy  hay  is  about  55  per  cent, 
digestible.  From  a  ton  of  timothy  hay  there  will  be 
about  790  pounds  of  dry  matter  in  the  manure.  The 
nitrogen,  phosphoric  acid,  and  potash  in  the  food  con- 
sumed are  nearly  all  returned  in  the  manure,  except 
under  those  conditions  which  will  be  noted.  The 
manure  from  a  ton  of  mixed  feed,  as  clover  and  bran, 
is  smaller  in  amount  but  more  concentrated  than  that 
produced  from  timothy.  In  a  ton  of  timothy  and 
in  a  ton  of  mixed  feed  (1500  Ibs.  clover,  500  Ibs.  bran) 
there  are  present : 

Timothy.  Mixed  feed. 

Lbs.  Lbs. 

Nitrogen 25.0  40.0 

Phosphoric  acid 9.0  24.0 

Potash 40.0  30.0 


FARM    MANURE  135 

The  nitrogen,  phosphoric  acid,  and  potash  in  these 
two  rations  are  retained  in  the  animal  body  in  dis- 
similar amounts  ;  10  per  cent,  more  of  these  elements 
being  retained  from  the  more  liberal  ration,  due  to 
more  favorable  conditions  for  growth.  Making  al- 
lowance for  this  fact  there  will  be  present  in  the  ma- 
nure from  the  mixed  feed  one-half  more  nitrogen,  and 
two  and  one-half  times  as  much  phosphoric  acid,  as 
in  the  manure  from  the  timothy  hay,  which,  _  free 
from  bedding,  contains  about  790  pounds  of  indigesti- 
ble matter  while  the  manure  from  the  mixed  feed  con- 
tains 760  pounds,  the  mixed  ration  being  more  digesti- 
ble. If  both  manures  contain  the  same  amount  of  ab- 
sorbents, the  manure  from  the  ton  of  mixed  clover 
and  bran  will  weigh  slightly  less,  but  contain  more 
fertility  than  that  from  the  timothy  hay. 

The  value  of  manure  can  be  accurately  determined 
from  the  composition  of  the  food  consumed  and 
the  care  which  the  manure  has  received.  Only  a 
small  amount  of  the  nitrogen  in  the  food  is  retained 
in  the  body.  The  larger  portion  is  used  for  repair 
purposes.  The  nitrogen  of  the  tissues  which  have 
been  renewed  is  voided  as  urea  in  the  liquid  excre- 
ments. Some  of  the  nitrogenous  compounds  of  the 
food  are  utilized  for  the  production  of  fat,  in  which 
case  the  nitrogen  is  voided  in  the  excrements.  The 
fact  that  but  little  of  the  nitrogen  and  mineral  matter 
of  the  food,  under  most  conditions,  is  retained  in  the 
body  may  be  observed  from  the  figures  of  Lawes  and 
Gilbert  relating  to  the  composition  of  the  flesh  added 
to  animals  while  undergoing  the  fattening  process.55 


136  SOILS   AND   FERTILIZERS 

INCREASE  DURING  FATTENING. 

Dry  Nitrogenous 

Water.          matter.  Fat.  matter.  Ash. 

Ox . 24.6  75.4  66.2  7.69  1.47 

Sheep 20.1  79.9  70.4  7.13  2.36 

Pig 22.0  78.0  71.5  6.44  0.06 

The  results  of  numerous  digestion  experiments 
show  that  when  the  food  undergoes  digestion  from  5 
to  15  per  cent,  of  the  nitrogen  is,  as  a  rule,  retained 
in  the  body.  The  nitrogen  of  the  food  is  utilized 
largely  to  replace  that  which  has  been  required  for 
vital  functions.  The  nitrogen  of  the  food  enters  the 
body,  undergoes  digestion  changes,  is  utilized  for 
some  vital  function,  and  is  then  voided  in  the  excre- 
ments. 

The  digestion  of  food  has  been  compared  to  the 
combustion  of  fuel :  the  undigested  products  of  the 
solid  excrements  represent  the  ashes,  and  the  urine 
represents  the  volatile  products.  When  wood  is  burn- 
ed the  nitrogen  is  converted  into  volatile  products. 
When  food  is  digested  and  utilized  by  the  body  the 
digestible  nitrogen  is  mainly  converted  into  urea, 
while  the  indigestible  nitrogen  is  voided  in  the  dung. 
In  the  solid  and  liquid  excrements  of  animals,  from 
80  to  95  per  cent,  of  the  nitrogen,  phosphoric  acid 
and  potash  of  the  food  are  present. 

171.  Composition  of  Solid  and  Liquid  Excrements 
Compared.  —  In  composition  the  liquid  excrements 
.differ  from  the  solids  in  having  a  much  larger  amount 
(.of  nitrogen  and  less  phosphoric  acid.56 


FARM    MANURE  137 


Water. 
Solids.  Liquids. 

Nitrogen. 
Solids.  Liquids. 

Phosphoric  acid. 
Solids.   Liquids. 

Potash. 
Solids. 

Percent.  Percent.  Percent.  Percent.  Percent. 

Per  cent. 

Per  cent 

Cows  .  . 

76 

89 

0.50 

1.  2O 

0-35 

... 

0.30 

Horses 

84 

92 

0.30 

0.86 

0.25 

O.  IO 

Pigs... 

80 

97.0 

0.6o 

0.80 

0-45 

0.  12 

0.50 

Sheep  . 

53 

86.5 

0-75 

1.40 

0.6  > 

0.05 

0.30 

The  nitrogen  in  the  food  consumed  influences  the 
amount  of  water  in  the  manure.  As  a  rule,  a  highly 
concentrated  nitrogenous  ration,  produces  a  higher  per 
cent,  of  water  in  the  manure  than  a  well-balanced 
ration.  There  is  but  little  phosphoric  acid  in  the 
liquid  excrements  of  horses  and  cows,  while  the  urine 
of  sheep  and  swine  contains  appreciable  amounts  of 
this  element. 

The  liquid  manure  is  more  constant  both  in  compo- 
sition and  amount  than  the  solid  excrements.  This 
fact  may  be  observed  from  the  following  table,  which 
gives  the  composition  of  the  solid  and  liquid  excre- 
ments from  hogs  when  fed  on  different  amounts  of 
grain.57 

Solid  excrements.  Liquid  excrements. 


g 

U 

a 

£3 

1  i 

S~s 

*       "2 

3 

o   • 

o  o 

^TJ   0 

lu 

S'-o  y 

S.3 

i  ^ 

I'gt 

*'«« 

Lbs. 

Kind  of  food  daily. 

1 

9f 

Barley  and  shorts 

8 

0-57 

0.72 

2.05 

0.06 

6 

Barley 

4 

0.43 

0.70 

2.06 

0.16 

si 

Corn  and  shorts. 

2\ 

0.80 

.... 

2.65 

O.2O 

6t 

Corn  

I* 

0.82 

0.80 

2.OS. 

0.20 

(In  each  experiment  the  amount  of  liquid  excrements  was  four  pounds.) 


138  SOILS   AND    FERTILIZERS 

The  amount  of  nitrogenous  waste  matter  in  the 
urine  is  nearly  the  same  whether  an  animal  be  gaining 
or  losing  in  flesh,  consequently  the  urine  is  more  con- 
stant in  both  composition  and  quantity  than  the  solid 
excrements. 

The  amount  and  composition  of  the  solid  excre- 
ments vary  with  the  amount  and  kind  of  food  con- 
sumed. If  the  food  is  indigestible  the  solid  excrements 
contain  a  larger  part  of  the  nitrogen  as  indigestible 
protein.  When  an  animal  is  properly  supplied  with 
food  for  all  purposes,  normal  conditions  exist,  and  the 
amount  of  nitrogen  voided  in  the  liquid  and  solid  ex- 
crements is  equal  to  that  supplied  in  the  food  con- 
sumed, except  in  the  case  of  growing  and  milk  pro- 
ducing animals. 

Experiments  at  the  Rothamsted  station  have  shown 
that  from  57  to  79  per  cent,  of  the  total  nitrogen  in 
the  food  of  farm  animals  is  voided  in  the  liquid  ex- 
crements, and  from  16  to  22  per  cent,  is  voided  in  the 
solid  excrements.  Nearly  all  of  the  mineral  elements 
in  the  food  is  voided  in  the  excrements,  less  than  four 
per  cent,  being  retained  in  the  body ;  in  the  case  of 
milk  cows  about  10  per  cent,  of  the  ash  in  the  food 
is  recovered  in  the  milk. 

172.  Manural  Value  of  Foods.  —  The  manurial 
value  of  a  fodder  is  determined  by  the  amount  of  nitro- 
gen, phosphoric  acid,  and  potash  present  in  the 
material.  Timothy  hay,  for  example,  has  a  manurial 
value  of  $5.30  per  ton,  which  means  that  if  the  nitro- 


FARM    MANURE  139 

gen,  phosphoric  acid,  and  potash  in  'the  timothy  hay 
were  purchased  in  commercial  forms  they  would  cost 
$5.30.  Lawes  and  Gilbert  estimate  that  80  per  cent, 
of  the  fertility  in  fodders  is,  as  a  rule,  returned  in  the 
manure. 

In  the  following  table  are  given  the  pounds  of 
nitrogen,  phosphoric  acid,  and  potash  per  ton  of 
some  food  materials  :57 

Nitrogen.    Phosphoric  acid.    Potash. 
Lbs.  lybs.  lybs. 

Timothy  hay 25  9  40 

Clover  hay 35  14  30 

Wheat  straw n  4  12 

Oat  straw 12  4  18 

Wheat : 45  20  12 

Oats 33  1 6  ii 

Barley 40  18  II 

Rye 42  20  13 

Flax '...  87  32  14 

Corn 32  14  8 

Wheat  shorts 48  31  20 

Wheat  bran 54  52  30 

Linseed  meal 100  35  25 

Cottonseed  meal 130  35  56 

Milk 10  33 

Cheese 90  23  5 

Live  cattle 53  37  3 

Potatoes 7  3  u 

Butter i  i  i 

Live  pigs.. 40  17  3 

173.  Commercial  Value  of  Manures.  —  When  the 
value  of  farm  manure  is  calculated  on  the  same  basis 
with  commercial  fertilizers  it  will  be  found  that 
stable  manure  is  worth  from  $2  to  #3.50  per  ton.  The 
value  of  the  increased  crops  resulting  from  its  use 


140  SOILS   AND   FERTILIZERS 

varies  with  conditions.  Farm  manures  favorably  in- 
fluence the  yield  of  crops  for  a  number  of  years. 
After  a  dressing  of  8  tons  of  farm  manure,  average 
prairie  land  will  yield  20  bushels  per  acre  more  corn 
the  first  year,  5  bushels  more  wheat  the  second  year, 
and  8  bushels  more  of  other  grains  the  third  year, 
with  slightly  increased  yields  in  subsequent  years. 
It  takes  about  three  years  for  the  manure  to  entirely 
repay  the  cost  of  its  application.  Its  influence  is  felt 
however  for  a  much  longer  time.  It  is  sometimes 
stated  that  the  phosphoric  acid  and  potash  in  stable 
manure  is  not  as  soluble  as  that  in  commercial 
fertilizers,  and  consequently  is  worth  less.  While 
not  so  soluble  in  the  form  of  manure,  it  frequently 
happens  that  the  phosphoric  acid  and  potash  in 
the  commercial  fertilizers  become,  through  fixation 
processes,  less  soluble  when  mixed  with  the  soil  than 
the  same  elements  in  stable  manure. 

Stable  manure  is  valuable  not  only  for  the  fertility 
contained  but  also  because  it  makes  the  inert  plant 
food  of  the  soil  more  available  and  exercises  such  a 
favorable  influence  on  the  water  supply  of  crops ; 
hence  it  is  justifiable  to  assign  the  same  value  to  the 
elements  in  well-prepared  farm  manures  as  to  those  in 
commercial  fertilizers. 

If  well-prepared  stable  manure  is  not  worth  $2.50 
per  ton,  then  too  much,  accordingly,  is  paid  for  com- 
mercial forms  of  plant  food. 

INFLUENCE  OF  AGE  AND   KIND  OF   ANIMAL 

174.  Manure  from  Young  and  Mature  Animals.  — 


AGE   AND   KIND   OF   STOCK  141 

The  manure  from  older  animals  is  somewhat  more 
valuable  than  that  from  young  animals,  even  when 
fed  the  same  kind  of  food.  This  is  because  more  of 
the  phosphoric  acid  and  nitrogenous  matters  are  re- 
tained in  the  body  of  a  young  animal.  It  is  not  so 
much  a  difference  in  digestive  power  as  a  difference 
in  retentive  power.  In  older  animals  the  proportion 
of  new  nitrogenous  tissue  produced  is  much  less  than 
in  young  animals,  and  more  of  the  nitrogen  of  the  food 
is  used  for  repair  purposes  and  subsequently  voided  in 
the  manure,  while  with  younger  animals  more  of  the 
nitrogen  of  the  food  is  retained  for  the  construction 
of  new  muscular  tissue. 

When  an  animal  is  neither  gaining  nor  losing  in 
flesh,  and  is  not  producing  milk,  an  equilibrium  is  es- 
tablished between  the  nitrogen  in  the  food  supply  and 
the  nitrogen  in  the  manure.  Under  such  conditions 
practically  all  of  the  nitrogen  of  the  food  is  returned 
in  the  manure.57 

175.  Cow  Manure.  —  A  milch  cow  when  fed  a  bal- 
anced ration,  will  make  from  60  to  70  pounds  of  solid 
and  liquid  manure  a  day,  of  which  20  to  30  pounds 
are  liquid  excrements.  The  solid  excrements  contain 
about  6  pounds  of  dry  matter.  When  a  cow  is  fed 
clover  hay,  corn  fodder,  and  grain,  about  half  of  the 
nitrogen  of  the  food  is  in  the  urine,  about  one-fourth 
in  the  milk,  and  the  remainder  in  the  solid  excre- 
ments. Hence,  if  the  solid  excrements  only  are  col- 
lected but  a  quarter  of  the  nitrogen  of  the  food  is  ob- 
tained, while  if  both  solids  and  liquids  are  utilized 


142  SOILS   AND   FERTILIZERS 

three-quarters  of  the  nitrogen  is  secured.  Cow  manure 
is  extremely  variable  in  composition,  and  is  the  most 
bulky  of  any  manure  produced  by  domestic  animals. 
A  well-fed  cow  will  produce  about  80  Ibs.  of  manure 
per  day,  including  absorbents. 

176.  Horse  Manure.  —  Horse  manure  contains  less 
water  than    cow  manure,  and    is  of  a  more    fibrous 
nature,  doubtless    due  to  the    horse    possessing    less 
power   for  digesting  cellulose  materials.     Horse  ma- 
nure readily  ferments  and  gives  off  ammonia  products. 
When  the  manure   becomes  dry,  fire-fanging  results, 
due  to  rapid  fermentation  followed  by  the  growth  of 
fungus  bodies.     Horse  manure  is  sometimes  consider- 
ed of  but  little  value.     This  is  because  it  so  readily 
deteriorates   in    value    and   when    used    it   has   lost 
much  of  its  nitrogen  by  fermentation.     When  mixed 
with    cow    manure,    both    manures    are    improved, 
the  rapid  fermentaion  of  the  horse  manure  is  checked, 
and  at  the  same  time  the  cow  manure  is  improved  in 
texture.     It  is  estimated  that  horses  void  about  three- 
fifths  of  their  manure  in  the  stable.     A  well-fed  horse 
at  ordinarily  hard  work  will  produce  about  50  pounds 
of  manure  per  day,  of  which  about  one-fourth  is  urine. 
A  horse  will  produce  about  6  tons  of  manure  per  year 
in  the  stable.     If  properly  preserved  and  used  it  is  a 
valuable,  quick-acting  manure,  but  if  allowed  to  fer- 
ment and  leach  it  gives  poor  results. 

177.  Sheep    Manure.  —  Sheep     produce   a  small 
amount  of  concentrated  manure,  containing  less  water 
than  that  produced  by  any  other  domestic  animal.     It 


AGE   AND    KIND    OF   STOCK  143 

readily  ferments  and  is  a  quick-acting  fertilizer. 
When  mixed  with  horse  and  cow  manure  the  mixture 
ferments  more  evenly.  Because  of  the  small  amount 
of  water,  sheep  manure  is  very  concentrated  in  composi- 
tion. It  is  valuable  for  general  gardening  purposes,  or 
whenever  a  concentrated  quick  acting  manure  is  desired. 

178.  Hog  Manure. — Hog  manure  is  not  constant 
in  composition  on  account  of  the  varied  character  of  the 
food    consumed.     The  manure   from   fattening  hogs 
which  are  well  fed  compares  favorably  in  composition 
and  value  with  the  manure  produced  by  other  ani- 
mals.    It  contains  a  high  per  cent,  of  water,  and,  like 
cow  manure,  may  be  slow  in  decomposing.     On  ac- 
count of  containing  so  much   water,  losses  by  leach- 
ing readily  occur.       From  a  given  weight  of  grain, 
pigs   produce   less  dry  matter    in  the   manure  than 
sheep  or  cows.     The  liquid   excrements  of  well-fed 
hogs  are  rich  in   nitrogen,  containing,  on  an  average, 
about  2  per  cent.    The  solid  excrements  when  leached, 
fermented  and  deprived  of  the  liquid  excrements  have 
but  little  value  as  fertilizer. 

179,  Hen  Manure.  —  Like  all  other  farm  manures 
hen  manure  is  variable  in  composition.     The  nitrogen 
is   present  mainly  in  the  form  of  ammonium   com- 
pounds.      This    makes    it    a    quick-acting    fertilizer. 
When  fowls  are  well-fed  the  manure  contains  about 
the  same  amount  of  nitrogen  as  sheep  manure.     Hen 
manure  readily  ferments,   and   if  not  properly  cared 
for  losses  of  nitrogen,  as  ammonia,  occur.     It  is  not 
advisable  to  mix  hard  wood  ashes  or  ordinary  lime 


144  SOILS   AND    FERTILIZERS 

with  hen  manure  because  the  ammonia  is  so  readily 
liberated  by  alkaline  compounds.  The  value  of  hen 
manure  is  due  to  its  being  a  quick-acting  fertilizer 
rather  than  to  its  containing  such  a  large  amount  of 
fertility.  A  hen  produces  about  a  bushel  of  manure 
per  year.56 

COMPOSITION  OF  HEN  MANURE. 

Per  cent. 

Water 57.50 

Nitrogen. 1.27 

Phosphoric  acid 0.82 

Potash. 0.28 

1 80.  Mixing  of  Solid  and  Liquid  Excrements. — 

The  solid  and  liquid  excrements,  when  properly  mixed, 
make  a  well-balanced  manure.  The  urine  alone  is 
not  a  complete  manure,  as  it  is  deficient  in  phosphoric 
acid  and  other  mineral  matter.  The  solid  excrements 
with  the  urine,  when  mixed  with  soil,  readily  undergo 
nitrification.  The  nitrogen  in  the  solid  excrements 
is  in  the  form  of  indigestible  protein,  and  is  rendered 
available  as  plant  food  more  slowly.  Land  heavily 
dressed  with  leached  manure  has  received  an  unbal- 
anced fertilizer  deficient  in  nitrogen  but  fairly  well 
supplied  with  mineral  matter.  A  soil  thus  manured 
may  fail  to  respond  because  of  the  unbalanced  char- 
acter of  the  manure. 

181.  Volatile   Products  from  Manure.  —  Fermen- 
tation of  manure  in  stables  results  in  the  production 
of  a  large  number  of  volatile  compounds  and  in  loss 
of  manurial  value.     Urea,  when  it  ferments,  produces 
ammonia,  which  combines  with   the   carbon   dioxide 
always  present  in  stables  in  liberal  amounts  as  a  pro- 


AGE    AND    KIND   OF   STOCK  145 

duct  of  respiration,  and  forms  ammonium  carbonate, 
a  volatile  compound.  When  the  stable  atmosphere 
becomes  charged  with  ammonium  carbonate  some  of 
it  is  deposited  on  the  walls  of  the  stable,  forming  a 
white  coating.  The  white  coating  found  on  harnesses 
and  carriages  stored  in  poorly  ventilated  stables,  is 
ammonium  carbonate.  Accumulations  of  manure  in 
the  stable  and  poor  ventilation  are  the  conditions  fav- 
orable to  the  production  of  this  compound. 

182.  Human  Excrements.  —  The  use  of  human  ex- 
crements as  manure  is  sometimes  advised,  and  in  some 
countries  they  are  extensively  used.  When  fresh, 
they  may  contain  a  high  per  cent,  of  nitrogen  and 
phosphoric  acid  ;  when  fermented,  a  loss  of  nitrogen 
has  occurred.  Heiden  estimates  that  in  a  year  1,000 
pounds  of  excrements  per  person  are  made,  which 
contain  #2.25  worth  of  fertility.59  For  sanitary  rea- 
sons, human  excrements  should  be  used  with  great  care. 
It  is  doubtful  with  the  abundance  and  cheapness  of 
plant  food  whether  their  extensive  use  as  manure  is 
advisable.  About  1840,  Leibig  expressed  the  fear  that 
the  essential  elements  of  plant  food  would  accumulate 
in  the  vicinity  of  large  cities  and  be  wasted,  and  that 
in  time  there  would  be  a  decline  in  fertility  due  to 
this  cause.60  Many  political  economists  shared  the 
same  fear.  Since  that  time  the  fixation  of  atmos- 
pheric nitrogen  through  the  agency  of  leguminous 
crops  has  been  discovered,  extensive  beds  of  sodium 
nitrate,  phosphate  rock  and  Stasfurt  salts,  have  been 
utilized  and  larger  areas  of  more  fertile  soils  have  been 

(10) 


146  SOILS   AND    FERTILIZERS 

brought  under  cultivation,  so  that  it  is  not  now  so 
essential  to  devise  means  for  utilizing  human  excre- 
ments as  manure. 

THE  PRESERVATION  OF  MANURE 

183.  Leaching. — Leaching  of  manure  is  the  greatest 
source  of  loss.  Experiments  by  Roberts  have  shown 
that  when  horse  manure  is  thrown  in  a  loose  pile  and 
subjected  to  the  joint  action  of  leaching  and  weather- 
ing it  may  lose  in  six  months  nearly  60  per  cent,  of 
its  most  valuable  fertilizing  constituents.  The  tab- 
ular results  are  as  follows  : l6 

April  25.  Sept.  28.  Loss. 

Lbs.  Lbs.  Per  cent. 

Gross  weight 4,000  1,73°  57 

Nitrogen 19.60  7.79  60 

Phosphoric  acid  ...       14.80  7.79  47 

Potash 36.0  8.65  76 

Value  per  ton $2.80  $i  .06 

Cow  manure,  on  account  of  its  more  compact  nature, 
does  not  leach  so  readily  as  horse  manure.  A  similar 
experiment  with  cow  manure,  conducted  at  the  same 
time,  showed  the  following  losses : 

April  25.  Sept  28.  LOSS. 

Lbs.  L,bs.  Per  cent. 

Gross  weight 10,000  5,125  49 

Nitrogen 47  28  41 

Phosphoric  acid             32  26  19 

Potash 48  44  8 

Value  per  ton  ....    $2.29  $1.60 

When  mixed  cow  and  horse  manure  was  compacted 
and  "  placed  in  a  galvanized  iron  pan  with  a  perfo- 
rated bottom  "  for  six  months,  the  losses  were  as  fol- 
lows : 


THE   PRESERVATION   OF   MANURE  147 

March  29.  Sept.  30.  Loss. 

Lbs.  L>bs.  Per  cent. 

Gross  weight 226  222 

Nitrogen 1.04  i.oi                3.2 

Phosphoric  acid  ••  0.61  0.58                4.7 

Potash 1.20  0.43              35.0 

Value  per  ton $2.38  $2.16 

1 84. Losses  by  Fermentation.  —  When  rapid  fer- 
mentation takes  place  in  manure,  appreciable  losses  of 
nitrogen  may  occur.  When  the  manure  is  well  com- 
pacted and  the  pile  is  so  constructed  as  to  prevent  the 
rapid  circulation  of  air  through  it,  losses  are  reduced 
to  the  minimum.  Experiments  have  shown  that 
when  leaching  is  prevented,  the  loss  of  nitrogen  by 
fermentation  of  the  mixed  manure  is  very  small. 
Under  poor  conditions  losses  by  fermentation  may 
exceed  15  per  cent.  Hen  manure,  sheep  man- 
ure and  horse  manure  suffer  the  greatest  losses  by 
rapid  fermentation.  When  extreme  conditions,  as  ex- 
cessive moisture,  drought  and  high  temperature,  fol- 
low each  other,  then  the  greatest  losses  occur. 

185.  Different  Kinds  of  Fermentation.  — The  large 
number  of  organisms  present  in  manure  all  belong  to 
one  of  two  classes  :  (i)  aerobic,  or  (2)  anaerobic.  The 
aerobic  ferments  require  an  abundant  supply  of 
air  in  order  to  carry  on  their  work.  When  deprived 
of  oxygen  they  become  inactive.  The  anaerobic  fer- 
ments require  the  opposite  condition.  They  become 
inactive  in  the  presence  of  oxygen  and  can  thrive  only 
when  air  is  excluded.-  In  the  center  of  a  well-con- 
structed manure  pile  anaerobic  fermentation  takes 
place  while  on  the  surface  aerobic  fermentation  is  act- 


148  SOILS   AND   FERTILIZERS 

ive.  The  anaerobic  ferments  prepare  the  way  for  the 
action  of  the  aerobic  bodies.  When  aerobic  fermenta- 
tion is  completed  the  organic  matter  is  converted  into 
water,  carbon  dioxide,  ammonia  and  •  allied  gases. 
From  what  has  been  said  regarding  the  action  of  these 
two  classes  of  ferments  it  is  evident  that  anaerobic 
fermentation  is  the  most  desirable. 


Fig.  26.     Fermentation  of  Manure. 

186.  Water  Necessary  for  Fermentation. — In  order 
to  produce    the  best  results  in  fermenting  manure, 
water  is  necessary.     If  the  manure  becomes  too  dry 
abnormal  fermentation  takes  place.     Water  is  always 
beneficial  on  manure  so  long  as  leaching  is  prevented; 
for  it  encourages  anaerobic  fermentation  by  excluding 
the  air.     An  excessive  amount  of  water,  such  as  falls 
on  piles  from  the  eaves  of  buildings,   is  more  than  is 
required  for  good  fermentation.     During  a  dry  time  it 
is  beneficial,   if  conditions  admit,  to  water  the  com- 
post pile. 

187.  Heat  Produced  During  Fermentation. — Dur- 
ing active  fermentation  of  horse  and  sheep  manure,  a 
temperature  of  175°   F.  may  be  reached  by  the  fer- 
menting mass.     Ordinarily,  however,  the  temperature 


THE   PRESERVATION   OF   MANURE  149 

of  the  manure  pile  ranges  from  110°  to  130°  F.  The 
highest  temperature  is  near  the  surface  where  fermen- 
tation is  most  rapid.  The  temperature  of  fermenta- 
tion may  be  sufficiently  high,  if  the  manure  is  mixed 
with  litter,  to  cause  spontaneous  combustion. 

1 88.  Composting  Manure  May  Improve  Its  Quality; 
— Composting  manure  so  that  leaching  and  rapid  fer- 
mentation do  not  take  place  may  improve  its  quality, 
making   it    more  concentrated.       Pound    for   pound, 
composted  manure  is  more  concentrated    than  fresh 
manure,   because,  if  properly  cared  for,  nearly  all  of 
the  nitrogen,  phosphoric  acid,  and  potash  of  the  orig- 
inal manure  are  obtained  in  a  smaller  bulk.     A  ton 
of  composted  manure  is  obtained  from  about  2,800 
pounds  of  stable  manure.     Composting  is  sometimes 
resorted  to  in  order  to  destroy  obnoxious  weed  seeds. 

Fresh  Composted 
manure.  manure. 

Per  cent.  Per  cent. 

Nitrogen 0.50  0.60 

Phosphoric  acid o.  28  0.39 

Potash 0.60  0.80 

In  composting  manure  it  should  be  the  aim  to  in- 
duce anaerobic  fermentation  by  excluding  the  air  and 
retaining  the  water.  This  can  be  accomplished  best 
by  using  mixed  manure  and  making  a  compact  pile, 
capable  of  shedding  water.  The  compost  pile  should 
be  shaded  to  secure  better  conditions  for  fermentation. 
If  the  pile  becomes  offensive  a  little  earth  on  the  sur- 
face will  absorb  the  odors. 

189.  Use  of  Preservatives. — The  use  of  preserva- 
tives, as  gypsum  and  kainit,  has  been  recommended 


150  SOILS   AND   FERTILIZERS 

to  prevent  fermentation  losses.  Opinions  differ  as  to 
their  value.  Moist  gypsum,  when  it  comes  in  contact 
with  ammonium  carbonate,  produces  ammonium  sul- 
phate, a  non-  volatile  compound, 


(NH4)2C03  +  CaS04=  (NH4)2SO4  +  CaCCX 

Gypsum  is  used  at  the  rate  of  about  one-half  pound 
per  day  for  each  animal.59  Experiments  have  shown 
that  it  may  prevent  a  loss  of  5  per  cent,  of  the  nitro- 
gen of  horse  manure.  It  may  be  safely  Iprinkled  in 
the  stalls  as  it  has  no  action  on  the  feet  of  animals. 
When  it  is  necessary  to  use  gypsum  as  a  fertilizer  it 
is  advantageous  to  use  it  in  stables.  It  is  not  advisable 
to  use  lime  in  any  other  form  than  the  sulphate.  Un- 
slaked lime  will  decompose  manure  and  liberate  am- 
monia. Neither  kainit  nor  gypsum  should  be  used 
when  manure  is  exposed  to  the  leaching  action  of 
rains.  Preservatives  cannot  be  made  to  take  the  place 
of  care  in  handling  manure  ;  they  should  be  used  only 
when  the  manure  receives  the  best  of  care. 

190.  Manure  Produced  in  Sheds  and  BoxStalls.  — 

Manure  produced  under  cover  as  in  sheds  and  box 
stalls  is  of  superior  quality  to  that  prepared  in 
any  other  way.  Losses  by  leaching  are  avoided, 
the  manure  is  compacted  by  the  tramping  of  the 
animals,  the  solid  and  liquid  excrements  are  more 
evenly  mixed  with  the  absorbents,  and  the  conditions 
are  favorable  for  anearobic  fermentation.  By  no  other 
system  is  there  such  a  large  percentage  of  the  fertility 
recovered.  Manure  from  well-fed  cattle,  when  col- 


THK   USE   OF   MANURE  15! 

lected  and  prepared  in  a  shed,  will  have  about  the 
following  composition  : 

Per  cent. 

Water 70.00 

Nitrogen 0.90 

Phosphoric  acid 0.60 

Potash 0.70 

191.  Value  of  Protected  Manure.  —Manure   that 
is  produced   under  cover  has  greater  crop-producing 
power  than  when  cared  for  in  any  other  way.     Ex- 
periments by   Kinnard  show  that  such  manure  pro- 
duced 4  tons  more  potatoes  per  acre  than  pile  manure, 
while  1 1  bushels  more   wheat  per  acre  were  obtained 
from   land  which  had  the  previous  year  received  the 
covered   manure  than  from  land  which  received  the 
uncovered  manure.62 

THE  USE  OF  MANURE 

192.  Direct  Hauling  to  Fields.— It  is  always  desir- 
able, whenever  conditions  allow,  to  draw  the  manure 
directly  to  the  field  and  spread  it,  rather  than  to  allow 
it    to   accumulate   about   barns  or  in    the   barnyard. 
When  taken  directly  to  the  field  from   the  stable  no 
losses  by  leaching  occur,  and  the  slight  loss  from  fer- 
mentation and  volatilization  of  the  ammonia  are  more 
than  offset  by  the  benefits  derived  from  the  action  of 
the  fresh  manure  upon  the  soil.       When  manure  un- 
dergoes fermentation  in  the  soil,  as  previously  stated, 
it  combines  with  the  mineral  matter  of  the  soil  and 
produces  humates.     The  practice  of  hauling  the  ma- 
nure directly  to  the  field  and  spreading  it  with  a  ma- 
nure  spreader  is  the  most  economical  way  of  caring 
for  it. 


152  SOILS   AND   FERTILIZERS 

With  scant  rainfall,  composting  the  manure  before 
spreading  is  necessary,  but  with  liberal  rainfall  it  is 
not  essential.  On  a  loam  soil  a  direct  application  of 
stable  manure  is  more  advisable  than  on  heavy  clay 
or  light  sandy  soils.  In  the  case  of  sandy  soils  there 
is  frequently  an  insufficient  supply  of  water  to  prop- 
erly ferment  the  manure.  Manure  sometimes  fails  to 
show  any  beneficial  effects  the  first  year  on  heavy  clay 
land,  because  of  the  slow  rate  of  decomposition,  but 
the  beneficial  effects  are  noticeable  the  second  and 
third  years. 

193.  Coarse  Manure  May  Be  Injurious.— The  ap- 
plication of  coarse  leached  manure  may  cause  the  soil 
to  be  so  open  and  porous  as  to  affect  the  water  supply 
of  the  crop,  by  introducing,  below  the  surface  soil,  a 
layer  of  straw,  which  breaks  the  capillary  connection 
with  the  subsoil.     Coarse  manure  and  shallow  spring 
plowing  are  sometimes  injurious,  where  fine  or  well- 
composted   manure  and  fall  plowing  are   beneficial. 
The  trouble  resulting  from  the  use  of  coarse  manure 
may  be  due  to  its  being  allowed  to  leach  before  it  is 
used,  so  that  it  does  not  readily  ferment  in  the  soil. 

194.  Manuring  Pasture  Land.  —  In  regions  where 
manure  decomposes  slowly,  it  is  sometimes  advisable 
to  spread  it  upon  pasture  land  as  a  top  dressing.     The 
manure  encourages  the  growth  of  grass,  so  that  it  ap- 
propriates plant  food  otherwise  lost ;  it  also  acts  as  a 
mulch  preventing  excessive  evaporation.     Then  when 
the  pasture  land  is  plowed  and  prepared  for  a  grain 
crop  it  contains  a  better  store  of  both  water  and  avail- 


THE   USE   OF   MANURE 


153 


able  plant  food.  The  manuring  of  pasture  lands  is 
one  of  the  best  ways  of  utilizing  the  manure  when 
trouble  arises  from  slow  decomposition. 


Fig.  27.     Manured  land. 


Fig.  28.     Unmanured  land. 

195.    Small    Manure   Piles    Undesirable.  —  It  is 

sometimes  the  custom  to  make  a  large  number  of 
small  manure  piles  in  fields.  This  is  a  poor  practice, 
for  it  entails  additional  expense  in  spreading  the  ma- 
nure, and  the  small  piles  are  usually  so  constructed 
that  heavy  losses  occur,  and  the  manure,  when  finally 
spread,  is  not  uniform  in  composition.  Oats  grown 
on  land  manured  in  this  way  present  an  uneven  ap- 
pearance. There  are  small  patches  of  thrifty,  overfed 
oats,  corresponding  to  the  places  occupied  by  the 
former  manure  piles,  while  large  areas  of  half-starved 
oats  may  be  observed. 


154  SOILS   AND    FERTILIZERS 

196.  Rate  of  Application. —  The  amount  of  manure 
that  should  be  applied  depends  upon  the  nature  of  the 
soil  and  the  crop.     On  loam  soils  intended  for  general 
truck  purposes  heavier  applications  may  be  made  than 
when  grain  is  raised.     For  general  farm  purposes,  6 
to  8  tons  per  acre  are  usually  sufficient.       It  is  better 
economy   to  make  frequent   light  applications   than 
heavier   ones    at   long   intervals.      When  manure  is 
used  frequently  the  soil  is  kept  in  a  more  even  state 
of  fertility,  and  losses  by  percolation,  denitrification, 
and  ammonification  are  prevented.      Too  often   the 
manure  is  not  evenly  distributed  about  the  farm,  fields 
adjacent  to  stables  are  heavily  manured,  while  those 
at  a  distance  receive  none. 

For  growing  garden  crops  20  tons  and  more  per 
acre  are  sometimes  used.  It  is  better,  however,  not 
to  use  stable  manure  in  excess  for  trucking,  but  to 
supplement  it  with  special  fertilizers  as  the  crops  may 
require.  Soils  which  contain  a  large  amount  of  cal- 
cium carbonate  will  not  become  acid  when  farm  ma- 
nure is  used,  and  hence  admit  of  more  frequent  and 
heavier  applications  than  soils  which  are  deficient  in 
this  compound.  The  lime  aids  fermentation  and  ni- 
trification. 

197.  Crops  Most  Suitable  for  Manuring.  —  Soils 
which  contain  a  low  stock  of  fertility  admit  of  manur- 
ing for  the  production  of  almost  any  crop.     Soils  well 
stocked   with   plant   food,  like   some  of   the   western 
prairie  soils,  which  are  in  need  of  manure  mainly  for 
its  physical  action,  will  not  admit  of  its  direct  use  on 


THE   USE   OF    MANURE  155 

all  crops.  On  a  prairie  soil  of  average  fertility  an 
application  of  well-rotted  manure  may  cause  wheat  to 
lodge.  When  manure  cannot  be  applied  directly  to 
a  crop,  it  may  be  used  indirectly.  It  never  injures 
corn  by  causing  too  rank  a  growth,  and  when  wheat 
follows  corn  which  has  been  manured  there  is  but 
little  danger  of  loss  from  lodging. 

On  some  soils  stable  manure  cannot  be  used  for 
growing  sugar-beets  ;  on  other  soils  it  does  not  seem  to 
exercise  an  injurious  effect.  Tobacco  is  injured  as  to 
quality  by  manure.  Crops,  as  flax,  tobacco,  sugar- 
beets  and  wheat,  which  do  not  admit  of  direct  appli- 
cations of  stable  manure  all  require  the  manuring  of 
preceding  crops.  When  in  doubt  as  to  what  crop  to 
apply  the  manure  to,  it  is  always  safe  to  apply  it  to 
corn,  and  then  to  follow  with  the  crop  which  would 
have  been  injured  by  its  direct  application. 

The  facts  that  coarse,  leached  manure  may  cause 
trouble  in  a  dry  season,  and  that  well-rotted  manure 
may  cause  grain  to  lodge,  are  no  substantial  reasons 
why  manure  should  be  wasted  as  it  frequently  is  in 
western  farming  by  being  burned,  used  for  making 
roads,  thrown  away  in  streams,  or  used  for  filling  up 
low  places. 

198.  Comparative  Value  of  Forage  and  Manure. — 

The  manure  from  a  given  amount  of  grain  or  fodder 
always  gives  better  results  than  the  food  itself  used 
directly  as  manure.  The  manure  from  a  ton  of  bran 
will  give  better  returns  than  if  the  bran  itself 
were  used.  This  is  because  so  little  of  the  fertility 


156  SOILS   AND   FERTILIZERS 

is  lost  during  the  process  of  digestion,  and  the 
action  of  the  digestive  fluids  upon  the  food  makes  the 
manure  more  readily  available  as  a  fertilizer  than  the 
food- which  has  not  passed  through  any  fermentation 
stages.  It  is  better  ecomony  to  use  products  as  lin- 
seed meal  and  cottonseed  meal  for  feeding  stock,  and 
to  take  good  care  of  the  manure,  than  to  use  the  mate- 
rials directly  as  fertilizer. 

199.  Lasting  Effects  of  Manure. — No  other  ma- 
nures make  themselves  felt  for  so  long  a  time  as  farm 
manures.     In  ordinary  farm  practice  an  application  of 
stable  manure  will  visably  affect  the  crops  for  a  num- 
ber of  years.     At  the  Rothamsted  Experiment  Station, 
records  have  been  kept  for  over  fifty  years  as  to  the 
effects   of   manures  upon  soils.     In   one   experiment 
farm  manure  was  used  for  twenty  years  and  then  dis- 
continued for  the  same  period.     It  was  observed  that 
when  its  use  was  discontinued  there  was  a  gradual  de- 
cline in  crop-producing  power,  but  not  so  rapid  as  on 
plots  where  no  manure  had  been  used.     The  manure 
which   had   been  applied  for  the  twenty-year  period 
made  itself  felt  for  an  ensuing  period  of  twenty  years. 

200.  Comparative  Value  of  Manure  Produced  on 
Two  Farms. — The  fact  that  there  is  a  great  differ- 
ence in  the  composition  and  value  of  manures  pro- 
duced on  different  farms  may  be  observed  from  the 
following  examples : 

On  one  farm  10  tons  of  timothy  are  fed.  The 
liquid  manure  is  not  preserved  and  25  per  cent, 
of  the  fertility  is  leached  out  of  the  solid  excre- 


THE   USE   OF   MANURE  157 

merits,  while  5  per  cent,  of  the  nitrogen  is  lost  by 
volatilization.  It  is  estimated  that  half  of  the  nitro- 
gen and  potash  of  the  food  is  voided  in  the  urine. 
On  account  of  the  scant  amount  and  poor  quality  of 
the  food  no  milk  or  flesh  is  produced. 

On  another  farm  7.5  tons  of  clover  hay  and  2.5  tons 
of  bran  are  fed.     The  liquid  excrements  are  collected 


3r|ariic:  Matter      Bj:§§§|' 


4.  Sja- 

Fig.  29.     Good  manure.  Fig.  30.     Poor  manure. 

i.  Nitrogen.     2.  Phosphoric  acid. 
3.  Potash.         4.  Mineral  matter. 

and  the  manure  is  taken  directly  to  the  field  and 
spread.  It  is  estimated  that  20  per  cent,  of  the  nitro- 
gen and  4  per  cent  of  the  phosphoric  acid  and  potasli 
are  utilized  for  the  production  of  flesh  and  milk. 

The  comparative  value  of  the  manures  from    the 
two  farms  is  as  follows : 


FARM  No.  i. 


In  10  tons  timothy, 
Lbs. 


Nitrogen  ..........................   250 

Phosphoric  acid  ....................     90 

Potash  ............................   400 


in  urine. 
250-=-  2  —  125  Ibs.  nitrogen 
400  -r-  2  =  200  Ibs.  potash 


158  SOILS   AND   FERTILIZERS 

FARM  No.  i. — (Continued}. 

Loss  by  Reaching. 

125  X  0.30  =  37.50  Ibs.  nitrogen 
90  X  0.25  =•  22.50  Ibs.  phosphoric  acid 
200  X  0-25  =  50  Ibs.  potash 

Total  loss. 

Lbs.  Per  cent. 

Nitrogen 162.5  65 

Phosphoric  acid 22.5  25 

Potash 250.0  62 

Present  in  final  product, 
manure  from  i  ton  timothy. 
Lbs. 

Nitrogen 8.75 

Phosphoric  acid 6.75 

Potash  15.00 

Relative  money  value $1.00 

FARM  No.  2. 

In  10  tons  mixed  feed. 
Lbs. 

Nitrogen 400 

Phosphoric  acid 240 

Potash 300 

LOSS,  sold  in  milk  and  retained  in  body. 
Lbs.  Per  cent. 

Nitrogen  400  X  °-2° 80  20 

Phosphoric  acid,  estimated...    10  4 

Potash 12  4 

Present  in  final  product, 

manure  from  i  ton  feed. 

Lbs. 

Nitrogen  32.0 

Phosphoric  acid 23.0 

Potash 26.0 

Relative  money  value $3-8o 

201.   Summary  of  Ways  in  which  Stable  Manure 
May  Be  Beneficial.  —  Farm  manures  act  upon  soils 
both  chemically  and  physically  : 
(a)  Chemically  : 

i.  By  adding  new  stores  of  plant  food  to  the  soil. 


THE   VALUE   OF   MANURE  159 

2.  By  acting  upon  the  soil,  forming  humates  and 
rendering  the  inert  mineral  plant  food  of  the  soil  more 
available. 

3.  By  raising  the  temperature  of  the  soil,  as  the  re- 
sult of  chemical  action. 

(b)  Physically: 

4.  By  making  the  soil  darker  colored. 

5.  By  enabling  soils  to  retain  more  water  and  to 
give  it  up  gradually  to  growing  crops. 

6.  By  improving  the  physical  condition  of  sandy 
and  clay  soils. 

7.  By  preventing  the  denuding  effects  of    heavy 
wind  storms. 


CHAPTER  VI. 


FIXATION. 

202.  Fixation,  a  Chemical  Change.  —  When  a  fer- 
tilizer is  applied  to  a  soil,   chemical   reaction   takes 
place  between  the  soil  and  the  fertilizer.     There  is 
a  general  tendency  for  the  soluble  matter  of  fertilizers 
to  undergo   chemical  change  and  become  insoluble. 
This  process  is  known  as  fixation.     If  a  solution  of 
potassium  chloride  be  percolated  through  a  column  of 
clay,  the  filtrate  will  contain  scarcely  a  trace  of  potas- 
sium chloride,  but    instead   calcium  and  other  chlo- 
rides. .  The  element  potassium  of  the  potassium  chlo- 
ride has  been  replaced  by  the  element  calcium  present 
in  the  soil.     As  a  result  of  this  change  between  the 
two  bases,  an  insoluble  compound  of  potash  is  formed 
in  the  soil. 

203.  Fixation  Due  to  Zeolites.  —  It  has  been  shown 
by   experiments,    particularly  by  those  of   Way  and 
Voechler,53  that  fixation  is  due  mainly  to  zeolitic  sili- 
cates  (See  section   62).     Sandy  soils  containing  but 
little  clay  have  only  feeble  power  of  fixation.     Clay 
soils  when  digested  with  hydrochloric  acid  to  remove 
the   zeolitic   silicates,    lose   their   power  of   fixation. 
The  fixation  of  potassium  chloride  and  the  liberation 
of  calcium  chloride  may  be  illustrated  by  the  follow- 
ing reaction  : 

Zeolite.  Zeolite. 

H,O  +  CaCl2 


etc 


FIXATION  l6l 

204.  Humus  May  Cause  Fixation.  —  Other  com- 
pounds of  the  soil  as  humus  and  calcium  carbonate 
also  take  an  important  part  in  fixation.     In  the  case 

of  humus,  a  union  takes  place  betweenthe  minerals 
in  the  fertilizers  and  the  organic  acids  formed  from 
the  decay  of  the  humus  in  the  soil,  resulting  in  the 
production  of  humates.  (See  Section  104.) 

205.  Soils  Possess  Different  Powers  of  Fixation. — 

All  soils  do  not  possess  the  power  of  fixation  to  the 
same  extent.  Heavy  clays  have  the  greatest  fixative 
power  while  sandy  soils  have  the  least.  Experi- 
ments have  shown  that  in  the  first  nine  inches  of 
soil,  from  2,000  to  8,000  pounds  per  acre  of  potash 
and  phosphoric  acid  may  undergo  fixation.54  Hence 
it  is  that  a  fertilizer,  after  being  applied  to  a  soil,  may 
be  entirely  changed  in  composition,  so  that  the  plant 
feeds  on  the  chemical  products  formed,  rather  than 
en  the  original  fertilizer. 

206.  Nitrates  Cannot  Undergo  Fixation.  —  Nitro- 
gen in  the  form  of  nitrates  or  nitrites  cannot  undergo 
fixation.     This  is  because  all  of  the  ordinary  forms  of 
nitrates  are  soluble.     If  potassium  nitrate  be  added  to 
a  soil,  calcium  or  sodium  nitrate  will  be  obtained  as 
the  soluble  compound.     The  potassium  undergoes  fix- 
ation, but  the  nitrate  radical  does  not.     Chlorides  also 
are  incapable  of  undergoing  fixation  because  all  of  the 
chlorides  found  in  soils  are  soluble. 

207.  Fixation    of   Ammonia.  —  Ammonium    com- 
pounds readily   undergo  fixation,  particularly  in  the 
presence  of  clay.,  (See  experiment  No.  15.)     Theam- 


1 62  SOILS   AND   FERTILIZERS 

moniuin  radical,  NH4,  like  potassium  is  capable  of  re- 
placing soil  bases.  After  undergoing  fixation,  the  am- 
monium compounds  readily  yield  to  nitrification  (See 
Section  145),  hence  they  serve  as  a  temporary  but 
important  form  of  insoluble  nitrogen.  The  gen- 
eral tendency  of  the  nitrogen  compounds  of  the  soil  is 
to  pass  from  insoluble  to  soluble  forms  through  pro- 
cesses of  decay,  and  to  resist  fixation  changes. 

1 08.  Fixation  May  Make  Plant  Food  Less  Avail- 
able. —  If  a  liberal  dressing  of  phosphate  fertilizer  be 
applied  to  a  heavy  clay  soil,  the  phosphoric  acid  which 
is  not  utilized  the  first  year  or  two  may  undergo  fix- 
ation to  such  an  extent  that  part  becomes  unavailable 
as  plant  food.      It  is  not  desirable  to  apply  heavy 
dressings  of  fertilizers  at  long  intervals  because  of  fix- 
ation.    It  is  always  best  to  make  lighter  applications 
and  more  frequently. 

109.  Fixation,  a  Desirable  Property  of  Soils.  —  If 
it  were  not  for  the  process  of  fixation,  soils  in  regions 
of  heavy  rains  would  soon  become  sterile.      On  ac- 
count of  the  plant  food  being  rendered  insoluble,  it  is 
retained  in  the  soil.     The  plant  food  which  undergoes 
fixation  is,  as  a  rule,  in  an  available  condition  or  may 
readily  become  so  by  cultivation  unless  the  soil  be  one 
of  unusual  composition.     The  process  of  fixation  in 
the  soil  regulates   the  supply  of  plant  food.      Many 
fertilizers,  if  they  did  not  undergo  this  process,  would 
be  injurious  to  crops  for  there  would  be  an  abnormal 
amount  of  soluble  alkaline  or  acid  compounds  which 
would  be  destructive.     The  process  of  fixation  first 
taking  place  removes,  to  a  great  extent,  the  injurious 


FIXATION  163 

water-soluble  salts,  particularly  when  the  reaction  is 
one  of  union  rather  than  replacement.  Then  the  plant 
is  free  to  render  soluble  its  own  food  in  quantities 
and  at  times  desired. 

Farm  manures  and  commercial  fertilizers  alike  un- 
dergo the  process  of  fixation  and,  in  studying  ferti- 
lizers, their  Action  upon  the  soil  and  the  products  of 
fixation  are  matters  of  prime  importance. 

Soil  water  obtained  by  leaching  soils  is  an  exceed- 
ingly dilute  solution  of  various  mineral  salts  and  organ- 
ic compounds.  Through  rock  disintegration,  mineral 
matter  is  rendered  soluble,  but  the  process  of  fix- 
ation prevents  accumulation  in  the  soil  solution  of 
compounds  of  such  elements  as  potassium  and  phos- 
phorus. As  a  result  of  disintegration  and  fixation, 
numerous  chemical  changes  take  place  iri  the  soil,  and 
the  soil  solution  is  an  important  factor  in  bringing  about 
these  reactions.  Many  of  the  phenomena  which  have 
been  studied  in  connection  with  solutions  in  physical 
chemistry,  take  place  in  the  soil.  Diffusion,  absorption, 
osmotic  pressure  and  ionization,88 — disassociation  of  the 
molecule  in  solution, — all  occur  in  soils  and  are  due 
largely  to  the  physical  and  chemical  action  of  the  soil 
solution.  The  soil  solution  from  different  soils  varies 
with  the  composition  and  disintegration  of  the  soil ; 
in  the  same  soil  at  different  times  variations  in  the 
composition  of  the  soil  solution  are  noticeable.  The  soil 
solution  is  more  important  as  an  agent  in  bringing 
about  chemical  and  physical  changes  in  the  soil  than 
as  a  storehouse  of  plant  food. 


CHAPTER  VII 


PHOSPHATE    FERTILIZERS 

210.  Importance  of  Phosphorus  as  Plant  Food. — 

Phosphorus  in  the  form  of  phosphates  is  one  of  the 
essential  elements  of  plant  food.  None  of  the  higher 
orders  of  plants  can  complete  their 
growth  unless  supplied  with  this 
element  in  some  form.  The  illus- 
tration (Fig.  31)  shows  an  oat  plant 
which  received  no  phosphates,  but 
was  supplied  with  all  of  the  other 
elements  of  plant  food.  As  soon  as 
the  phosphates  stored  up  in  the 
seed  had  been  utilized,  the  plant 
ceased  to  grow,  and  after  a  few 
weeks,  died  of  phosphate  starvation, 
having  made  the  total  growth 
shown  in  the  illustration.  All  crops 
demand  their  phosphates  at  an  early 
stage  in  their  development.  Wheat 
Fig.  31.  takes  up  eighty  per  cent,  of  its 

Oat  plant  grown      phosphoric  acid  in  the  first  half  of 

without  phosphorus  .  .     -  ,  .,         , 

the  growing  period,37  while  clover 
has  assimilated  all  of  its  phosphoric  acid  by  the 
time  the  plant  reaches  full  bloom.43  Phosphates  ac- 
cumulate, to  a  great  extent,  in  the  seeds  of  grains  and 
hence  are  sold  from  the  farm  when  grain  farming  is 
extensively  followed.  All  crops  are  very  sensitive  to 


PHOSPHATE    FERTILIZERS  165 

the  absence  of  phosphates  ;  an  imperfect  supply  re- 
sults in  the  production  of  light  weight  grains.  The 
nitrogen  and  phosphates  are  to  a  great  extent  stored 
up  in  the  same  parts  of  the  plant,  particularly  in  the 
seed,  which  is  richer  in  both  nitrogen  and  phosphorus 
than  is  any  other  part.  Nitrogen  is  the  chief  element 
of  protein,  while  phosphorus  is  necessary  to  aid  in 
transporting  the  protein  compounds  through  the  cell 
walls  of  plants.  In  speaking  of  the  phosphorus  in 
plants  and  in  fertilizers,  as  well  as  in  soils,  the  term 
phosphoric  acid  or  phosphoric  anhydride  is  used. 
This  is  because  phosphorus  is  an  acid-forming  ele- 
ment and,  as  already  explained,  the  anhydride  of  the 
element  is  always  considered  instead  of  the  element 
itself. 

211.  Amount  of  Phosphoric  Acid  Removed  in 
Crops. — The  amount  of  phosphoric  acid  removed 
in  an  acre  of  different  farm  crops  ranges  from  18  to  30 
pounds : 

Phosphoric  acid 
per  acre. 
Lbs. 

Wheat,  20  bu 12.5 

Straw,  2,000  Ibs 7.5 

Total .    20.0 

Barley,  40  bu 15 

Straw,  3,000  Ibs 5 

Total 20 

Oats,  50  bu 12 

Straw,  3,000  Ibs 6 

Total 18 


166  SOILS    AND   FERTILIZERS 

Phosphoric  acid 
per  acre. 
Lbs. 

Corn,  65  bu 18 

Stalks,  4,000  Ibs 4 

Total 22 

Peas,  3,500  Ibs 25 

Red  Clover,  4,000  Ibs 28 

Potatoes,   150  bu . . . 20 

Flax,  15  bu 15 

Straw,  i, 800  Ibs 3 

Total... 18 

212.  Amount  and  Source  of  Phosphoric  Acid  in 
Soils. — To  meet  the  demand  of  growing  crops  for  25 
pounds  of  phosphoric  acid  per  acre,  there  are  present 
in  soils  from  1,000,  and  less,  to  8,000  pounds  of  phos- 
phoric acid  per  acre,  of  which,  however,  only  a  frac- 
tion is  available  as  plant  food  at  any  one  time.  The 
availability  of  phosphoric  acid  is  a  factor  which  has  a 
great  deal  to  do  in  determining  crop-producing  power. 
Many  soils  contain  a  large  amount  of  total  phosphoric 
acid  which  has  become  unavailable,  because  of  poor 
cultivation  and  the  absence  of  stable  manure  and  lime 
to  combine  with  the  phosphates  and  render  them 
available. 

The  phosphates  in  soils  are  derived  mainly  from 
the  disintegration  of  phosphate  rock  and  from  the 
remains  of  animal  life.  The  phosphate  deposits 
found  in  various  localities  are  supposed  to  have  been 
derived  either  from  the  remains  of  marine  animals  or 
from  sea-water  highly  charged  with  soluble  phos- 


PHOSPHATE    FERTILIZERS  167 

phates.  These  deposits  have  been  subjected  to 
various  geological  and  climatic  changes  which  have 
resulted  in  the  formation  of  soft  phosphate,  pebble 
phosphate  and  rock  phosphate.63 

213.  Commercial  Forms  of  Phosphoric  Acid. — The 
commercial  sources  of  phosphate  fertilizers  are  :  (i) 
phosphate  rock,  (2)  bones  and  bone  preparations,  (3) 
phosphate  slag  and  (4)  guano.  With  the  exception 
of  phosphate  slag  and  guano,  the  prevailing  form  of 
phosphorus  is  tricalcium  phosphate.  Before  being 
used  for  commercial  purposes,  the  tricalcium  phos- 
phate, which  is  insoluble  and  unavailable,  is  treated 
with  sulphuric  acid  which  produces  monocalcium 
phosphate,  a  soluble  and  available  form  of  plant  food. 
Cas  (P04)2  +  2H2S04  +  5H20  =  CaH4(PO4)2  +  H2O  + 
2CaS04,2H20. 

In  making  phosphate  fertilizers  from  bones  or  phos- 
phate rock  an  excess  of  the  rock  is  used  so  that  there 
will  be  no  free  acid  in  the  fertilizer  to  be  injurious  to 
vegetation. 

The  usual  form  in  which  calcium  phosphate  is 
found  in  nature  is  tricalcium  phosphate,  Cas(PO4)2. 
Unless  associated  with  organic  matter  or  salts  which 
render  it  soluble  it  is  of  but  little  value  as  plant  food. 
When  tricalcium  phosphate  is  treated  with  sulphuric 
acid,  monocalcium  phosphate,  CaH  (PO  )2,  is  formed. 
This  compound  is  soluble  in  water  and  directly  avail- 
able as  plant  food.  When  tricalcium  and  monocal- 
cium phosphate  are  brought  together  in  a  moist  con- 
dition, dicalcium  phosphate  is  produced. 


168  SOILS   AND   FERTILIZERS 


Cas(P04).  +  CaH4(P04)2  = 
Another  form  of  phosphate  of  lime,  met  with  in  basic 
phosphate  slag,  is  tetracalcium  phosphate,  (CaO)4P2O5. 

214.  Reverted  Phosphoric  Acid.  —  When  mono-  and 
tricalcium  phosphate  react,  the  product  is  known  as 
reverted  phosphoric  acid,  which  is  insoluble  in  water, 
but  is  not  in  such  form  as  to  be  unavailable  as  plant 
food.     It   is  generally  considered    that   the  reverted 
phosphoric   acid   is   available   as    plant   food.     It    is 
soluble  in  a  dilute  solution  of  ammonium  citrate,  and 
is  sometimes  spoken  of  as  citrate-soluble  phosphoric 
acid.     Citrate-soluble   phosphoric   acid   may  also   be 
formed  by  the  action,  upon  the  monocalcium  phos- 
phate,  of  iron   and  aluminum  compounds  present  as 
impurities-  in  the  phosphate  rock.     This  process  is  a 
fixation  change,   as  described  in  Chapter  VI.     In  an 
old  fertilizer  there  may  be  present  citrate-soluble  phos- 
phoric acid  in  two  forms,  as  dicalcium  phosphate  and 
as  hydrated  phosphates  of  iron  and  aluminum.     The 
citrate-soluble  phosphoric  acid  in  fertilizers  is  not  all 
equally  valuable  as  plant  food  because  of  the  different 
phosphate  compounds  that  may  be  dissolved  by  this 
solvent. 

215.  Available   Phosphoric   Acid.  —  As   applied  to 
fertilizers,  the  term  available  phosphoric  acid  includes 
the  water-soluble  and  citrate-soluble  phosphoric  acid. 
These  solvents  do  not,  under  all   conditions,  make  a 
sharp  distinction  as  to  the  available  and  unavailable 
phosphoric    acid    when   it    comes    to    plant    growth. 
Some  forms  of  bones  which  are  insoluble  in  an  am- 


PHOSPHATE   FERTILIZERS  169 

inonium  citrate  solution  are  available  as  plant  food, 
an'd  then  again  some  forms  of  aluminum  phosphate 
which  are  soluble  are  of  but  little  value  as  plant  food. 
The  terms  available  and  unavailable  phosphoric  acid, 
as  applied  to  commercial  fertilizers,  refer  to  the 
solubility  of  the  phosphates,  and  as  a  general  rule  the 
value  of  the  phosphates  as  plant  food  is  in  accord  with 
their  solubility.  The  more  insoluble  the  less  valu- 
able the  material. 

216.  Phosphate   Rock.  — Phosphate  rock  is   found 
in  many  parts  of  the  United  States,  particularly  in 
South  Carolina,    North   Carolina,    Florida,    Virginia 
and  Tennessee.     The  deposits  occur  in  stratified  veins, 
as  well  as  in  beds  and   pockets.     There  are  different 
types   of   phosphates  as    hard   rock,  soft  rock,    land 
pebble  and  river  pebble.     The  pebble  phosphates  are 
found  either  on  land  or  collected,  in   cavities  in  the 
water  courses,  and  are  generally  spherical  masses  of 
variable    size.      The   soft    rock    phosphate    is   easily 
crushed,  while  the  hard  rock  requires  pulverizing  with 
rock  crushers.     Phosphate  rock  usually  contains  from 
40  to  70  per  cent,  of  calcium  phosphate,  the  equiva- 
lent of  from  17  to  30  per  cent,  phosphoric  acid.     The 
remaining  30  to  60  per  cent,  is  composed  of  fine  sand, 
limestone,  alumina  and  iron  compounds,  with  other 
impurities,  which  often  render  a  phosphate  unsuitable 
for  manufacture  into  high-grade  fertilizer.     Raw  phos- 
phate rock  is  sold  at  the  mines  for  from  $1.75  to  $4.50 
per  ton. 

217.  Superphosphate. —  Pulverized  rock  phosphate 


1  70  SOILS   AND   FERTILIZERS 

known  as  phosphate  flour,  is  treated  with  commercial 
sulphuric  acid  to  obtain  soluble  monocalcium  phos- 
phate. The  amount  of  sulphuric  acid  used  is  deter- 
mined by  the  composition  of  the  rock.  Impurities  as 
calcium  carbonate  and  calcium  fluoride  react  with  sul- 
phuric acid  and  cause  a  loss  of  acid.  Ordinarily,  a 
ton  of  high-grade  phosphate  rock  requires  a  ton  of 
sulphuric  acid.  The  mixing  is  done  in  lead-lined 
tanks.  A  weighed  amount  of  phosphate  flour  is 
placed  in  the  tank,  and  the  sulphuric  acid  added, 
through  lead  pipes,  from  the  acid  tower.  The  mixing 
of  the  acid  and  phosphate  is  done  with  a  mechanical 
mixer,  driven  by  machinery.  From  the  mixing  tank 
the  material  is  passed  into  other  large  tanks,  where 
two  or  three  days  are  allowed  for  the  completion  of 
the  reaction.  When  the  mass  solidifies,  it  is  ground 
and  sold  as  superphosphate.  In  the  manufacture  of 
superphosphate,  gypsum  (CaSO4.2H2O)  is  always  pro- 
duced. A  ton  of  superphosphate  prepared  from  high- 
grade  rock  in  the  way  outlined  will  contain  about  40 
per  cent,  of  lime  phosphate,  equivalent  to  18  per  cent. 
phosphoric  acid.  If  a  poorer  quality  of  rock  is  used 
a  proportionally  smaller  amount  of  phosphoric  acid  is 
obtained.  A  more  concentrated  superphosphate  is  ob- 
tained by  producing  phosphoric  acid  from  the  phos- 
phate rock,  and  then  allowing  the  phosphoric  acid  to 
act  upon  fresh  portions  of  the  rock,  the  reactions  be- 
ing as  follows  :  64 


Ca  (P04X  +  3H3S04  =  3CaSO    +  2H3(PO4). 
Ca(PO  ),  +  4H  PO  3H,0  =  3[CaH  (PO4).,H.O]. 
Ca  (PO  ;>.+  2H3P04+  i2H,0=3[Ca,H,(P04).,4H.O]. 


PHOSPHATE   FERTILIZERS  17 1 

The  phosphoric  acid  is  separated  from  the  gypsum  be- 
fore acting  upon  the  phosphate  flour.  In  this  way, 
superphosphate  containing'  from  35  to  45  per  cent, 
of  phosphoric  acid  is  produced.  When  fertilizers  are 
to  be  transported  long  distances  this  concentrated 
product  is  preferable.  The  terms  ( acid  '  and  ( super- 
phosphate '  have  been  generally  used  to  designate 
both  the  first  product  produced  by  the  action  of  sul- 
phuric acid  and  that  produced  by  phosphoric  acid,  but 
of  late  there  is  a  tendency  to  restrict  the  term  ( acid 
phosphate '  to  the  product  formed  by  the  action  of 
sulphuric  acid,  and  the  term  '  super-phosphate '  to  the 
concentrated  product  formed  by  the  action  of  phos- 
phoric acid. 

218.  Commercial  Value  of  Phosphoric  Acid. — The 
commercial  value  of  phosphoric  acid  in  fertilizers  is 
determined  by  the  value  of  the  crude  phosphate  rock, 
cost  of  grinding  and  treating  with  sulphuric  acid,  and 
cost  of  transportation.     The  price  of  phosphoric  acid 
in  superphosphates  usually  ranges  from  5  to  6  cents 
per   pound.     The   field    value,  that  is   the  increased 
yields  obtained  from  the  use  of  superphosphates,  may 
not  be  in  accord  with  the  commercial  value  because  so 
many  conditions  govern  their  use.     The  phosphoric 
acid   obtained   from   feed-stuffs  is  usually  considered 
worth  about  a  cent  a  pound  less  than  that  from  super- 
phosphates.    Water-soluble  phosphoric  acid  is  general- 
ly rated  a  half  cent  per  pound  higher  than  citrate-sol- 
uble phosphoric  acid. 

219.  Phosphate  Slag.  —  In  the  refining  of  iron  ores 


172  SOILS    AND    FERTILIZERS 

by  the  Bessemer  process,  the  phosphorus  in  the  iron  is 
removed  as  a  basic  slag.  The  lime,  which  is  used  as  a 
flux,  melts  and  combines  with  the  phosphorus  of  the 
ore,  forming  phosphate  of  lime.  The  slag  has  a  varia- 
ble composition.  The  process  by  which  the  phos- 
phorus of  pig  iron  is  removed-and  converted  into  basic 
phosphate  slag  is  known  as  the  Thomas  process,  and 
the  product  is  sometimes  called  Thomas'  slag.  At  the 
present  time  but  little  basic  slag  is  produced  for  fer- 
tilizer purposes  in  this  country.  In  Germany  and 
some  other  European  countries  large  amounts  are 
used.  Phosphate  slag  is  ground  to  a  fine  powder  and 
is  applied  directly  to  the  land,  without  undergoing 
the  sulphuric  acid  treatment.  The  phosphoric  acid  is 
present  mainly  in  the  form  of  tetracalcium  phosphate, 
(CaO)4P,05. 

220.  Guano  is  the  Spanish  for  dung,  and  is  a  concen- 
trated form  of  nitrogenous  and  phosphate  manure  of 
interest -mainly  on  account  of  its  historic  significance. 
It  is  a  mixture  of  sea-fowl  droppings,  accumulating 
along  the  seacoast  in  sheltered  regions,  with  dead 
animals  and  debris,  which  has  undergone  fermen- 
tation. Guano  and  is  concentrated  in  both  nitro- 
gen and  phosphoric  acid.  The  introduction  of  guano 
into  Europe  marked  an  important  period  in  agri- 
culture, inasmuch  as  its  use  demonstrated  the  action 
and  importance  of  concentrated  fertilizers.  All  of  the 
best  beds  of  guano  have  been  exhausted  and  only  a 
little  of  the  poorer  grades  are  now  found  on  the  mar- 
ket. The  best  qualities  of  guano  contained  from  12 


PHOSPHATE    FERTILIZERS  173 

to  15  per  cent,  of  phosphoric  acid,  10  to  12  per  cent, 
of  nitrogen,  and  from  5  to  7  per  cent,  of  alkaline  salts. 

BONE  FERTILIZERS 

221.  Raw  Bones  contain,  in  addition  to  phosphate 
of  lime,  Ca  (PO  )2,  organic  matter  which  makes  them 
slow  in  decomposing  and  slow  in  their  action  as  a  fer- 
tilizer.    Before  being  used  as  a  fertilizer  they  should  be 
fermented  in  a  compost  heap  with  wood  ashes  in  the 
following  way,  a  protected  place  being  selected  so  that 
no  losses  from  drainage  will  occur.     A  layer  of  well- 
compacted  manure  is  covered  with  wood  ashes,   the 
bones  are  then  added   and  well  covered   with  manure 
and  wood  ashes.     From  three  to  six  months  should 
be  allowed  for  the  bones  to  ferment.     The  large,  coarse 
pieces  may  then  be   crushed  and  are  ready  for   use. 
The  presence  of  fatty  material  in  a  fertilizer  retards  its 
action  because  fat  is  so  slow  in  decomposing.      Bones 
from  which  the  organic  matter  has  been  removed  are 
more    active  as  a   fertilizer  than  raw  bones.     Bones 
contain  from  18  to  25  per  cent,  of  phosphoric  acid  and 
from  2  to  4  per  cent,   of  nitrogen.     The  amount  and 
value  of  the  citrate-soluble  phosphoric  acid  are  extre- 
mely variable. 

222.  Bone  Ash  is  the  product  obtained  when  bones 
are  burned.     It  is  not  extensively  used  as  a  fertilizer 
because  of  the  greater  commercial  value  of  bone-black. 
It  contains  about  36  per  cent,  of  phosphoric  acid,  and 
is  more  concentrated  than  raw  bones. 

223.    Steamed  Bone.  —  Raw  bones  are  subjected  to 
superheated  steam  to  remove  the  fat  and  ossein  to  be 


174  SOILS   AND   FERTILIZERS 

used  for  making  soap  and  glue ;  they  are  then  pul- 
verized and  sold  as  fertilizer  under  the  name  of  bone 
meal,  which  contains  from  1.5  to  2.5  per  cent,  of  nitro- 
gen and  from  22  to  29  per  cent,  of  phosphoric  acid. 
Steamed  bone  makes  a  more  active  fertilizer  than  raw 
bone.  Occasionally,  well  prepared  bone  meal  is  used 
for  feeding  pigs  and  fattening  stock  in  the  same  way 
that  flesh  meal  is  used. 

224.  Dissolved  Bone.  —  When    bones  are    treated 
with  sulphuric  acid  as  in  the  manufacture  of   super- 
phosphates the  product  is  called  dissolved  bone.     The 
tricalcium    phosphate    undergoes  a  change   to    more 
available  forms,  as  described,  and  the  nitrogen  is  ren- 
dered more  available.     Dissolved  bone  contains  from 
2  to  3  per  cent,  of  nitrogen  and  from  15  to  17  percent, 
of  phosphoric  acid. 

225.  Bone-black.  —  When  bones  are  distilled  bone- 
black  is  obtained.     It  is  extensively  employed  for  re- 
fining sugar,  and  after  it  has  been  used  and  lost  its 
power  of  decolorizing  solutions,  it  is  sold  as  fertilizer. 
It  contains  about  30  per  cent,  phosphoric  acid  and  is  a 
concentrated  phosphate  fertilizer. 

226.  Use  of  Phosphate  Fertilizers.  — The  amount 
of  phosphoric  acid  advisable  to  apply  to  crops,  varies 
with  the  nature  of  the  soil  and  the  kind  of  crop  to  be 
produced.     On  a  poor  soil  400  pounds  of  acid-phos- 
phate per  acre  is  an  average  application.     It  is  usually 
applied  as  a  top  dressing  just  before  seeding,  and  may 
be  placed  near  the  hills  of  corn  or  potatoes,,  but  not  in 
contact  with  the  seed.     It  is   not  advisable   to  make 


PHOSPHATE   FERTILIZERS  175 

heavy  applications  of  superphosphates  at  long  inter- 
vals, because  the  process  of  fixation  may  take  place  to 
such  an  extent  that  crops  are  unable  to  utilize  the  fer- 
tilizer. Lighter  and  more  frequent  applications,  as 
100  to  200  pounds  per  acre,  are  preferable.  Phos- 
phates should  not  be  mixed  with  lime  carbonate 
before  spreading  ; 22  it  is  best  to  apply  the  fertilizer 
directly  to  the  land.  Phosphates  may  be  used  in  con- 
nection with  farm  manures.  Many  soils  which  con- 
tain liberal  amounts  of  phosphoric  acid  are  im- 
proved by  phosphate  dressing  of  75  pounds  per  acre. 
Such  soils,  however,  should  be  more  thoroughly 
cultivated,  and  manured  with  farm  manures,  to 
make  the  phosphates  available.  There  is  frequently 
an  apparent  lack  of  phosphoric  acid  in  a  soil 
when  in  reality  the  trouble  is  due  to  other  causes, 
as  lack  of  organic  matter  to  combine  with  the  phos- 
phates or  to  a  deficiency  of  lime.  Before  using  phos- 
phate fertilizers,  careful  field  tests  should  be  made  to 
determine  if  the  soil  is  in  actual  need  of  available 
phosphoric  acid.  Directions  for  making  these  tests 
are  given  in  Chapter  X. 

227.  How  to  Keep  the  Phosphoric  Acid  Available. 
— Phosphoric  acid  associated  with  organic  matter  in 
a  moderately  alkaline  soil,  is  more  available  than  that 
in  acid  soils.  Soft  phosphate  rock  may  be  mixed  with 
manure  or  materials  like  cottonseed  meal  and  made 
slowly  available  for  crops.  Soils  which  contain  a 
good  stock  of  phosphoric  acid,  when  kept  well  ma- 
nured, and  occasionally  limed  if  necessary,  have  a  lib- 
eral supply  of  available  phosphoric  acid.  As  an  illus- 


176  SOILS    AND    FERTILIZERS 

tration,  the  following  example  of  two  soils  from  ad- 
joining farms,  which  have  been  cropped  and  manured 
differently,  may  be  cited  :31 

Soil  well  manured  No  manure  and 

and  crops  continuous  wheat 
rotated.  raising. 

Per  cent.  Per  cent. 

Total  phosphoric  acid 0.20  0.20 

Humus 4.25  1.62 

Humic  phosphoric  acid--  0.06  0.02 

It  is  more  economical  to  keep  the  insoluble  phos- 
phoric acid  of  the  soil  in  available  forms  by  the  use  of 
farm  manures,  lime,  rotation  of  crops  and  thorough 
cultivation,  than  it  is  to  purchase  superphosphates  in 
commercial  forms. 


CHAPTER  VIII 


POTASH  FERTILIZERS 

228.  Potassium  an   Essential   Element  of  Plant 
Food.  —  Potassium  is  one  of  the  three  elements  most 

essential  as  plant  food.  In  its  ab- 
sence plants  are  unable  to  develop. 
Oats  seeded  in  a  sterile  soil  from 
which  potash  only  was  withheld 
made  the  total  growth  shown  in 
the  illustration  (Fig.  32).  When 
potash  is  present  in  the  soil  in' 
liberal  amounts  and  associated 
with  other  essential  elements  vig- 
orous plants  are  produced.  Potash 
like  phosphoric  acid  and  nitrogen 
is  utilized  by  crops  in  the  early 
stages  of  growth.  Potassium 
does  not  accumulate  in  seeds  to 
the  same  extent  as  phosphoric 
acid  and  nitrogen,  but  is  present 
Fig.  32.  Oat  plant  mainly  in  stems  and  leaves,  con- 
grown  without  potash.  Sequently  when  straw  crops  are 
utilized  in  producing  manure  the  potash  is  not  lost  or, 
as  in  the  case  of  nitrogen,  sold  from  the  farm.  But 
with  ordinary  grain  farming  excessive  losses  of  potash 
do  occur,  particularly  when  the  straw  is  burned  and 
the  ashes  are  wasted. 

229.  Amount  of  Potash  Removed  in  Crops. — In 

(12) 


178  SOILS   AND   FERTILIZERS 

grain  crops  from  35  to  60  pounds  of  potash  per  acre 
are  removed  from  the  soil.  For  grass  crops  more  pot- 
ash is  required  than  for  grains,  while  roots  and  tubers 
require  more  than  grass.  The  approximate  amount 
of  potash  removed  in  various  crops  is  given  in  the 
following  table  :38 

Potash  per  acre 
tt>s. 

Wheat,  20  bu 7 

Straw,  2,000  Ibs 28 

Total 35 

Barley,  40  bu 8 

Straw,  3,000  Ibs 30 

Total 38 

Oats,  50  bu 10 

Straw,  3,000  Ibs 35 

Total 45 

Corn,  65  bu 15 

Stalks,  3,000  Ibs 45 

Total 60 

Peas,  30  bu 22 

Straw,  3,500  Ibs 38 

Total 60 

Flax,  15  bu 8 

Straw,  i, 800  Ibs 19 

Total 27 

Mangels,  10  tons 15° 

Meadow  hay,  i  ton 45 

Clover  hay,  2  tons 66 

Potatoes,  150  bushels 75 


POTASH   FERTILIZERS  179 

230.  Amount   of  Potash  in  Soils.  —  In  ordinary 
soils  there  are  from  3,500  to  12,000  pounds  of  potash 
per  acre  to   the  depth  of  one  foot.     Many  soils  with 
apparently  a  good  stock  of  total  potash  give  excellent 
results  when  a  light -dressing  of  potash  salts  is  applied. 
The  amount  of  available  potash  in  the  soil  is  more 
difficult   to   estimate  than    the  available    phosphoric 
acid.     There  is  a  great  difference  in  crops  as  to  their 
power   of   obtaining   potash.     Some  require   greater 
help  in  procuring  this  element  than  others.     A  lack 
of  available  potash   is  sometimes  indirectly  due  to  a 
deficiency  of  lime  or  other  alkaline  matter  in  the  soil, 
which  prevents  the  necessary  chemical  changes  taking 
place  in  order  that  the  potash  may  be  liberated  as 
plant  food. 

231.  Sources   of   Potash    in   Soils.  —  The   main 
source  of  the  soil's  potash  is  feldspar,  which,  after  dis- 
integration, is  broken  up  into  kaolin  and  potash  com- 
pounds.    Mica  and  granite  also,  in  some  localities, 
contribute   liberal    amounts.     A   valuable   source   of 
potash    are    the   zeolitic    silicates.     The   amount   of 
water-soluble  potash  in  soils,  except  in  alkaline  soil, 
is  extremely  small.     By  the  action  of  many  fertilizers 
the  potash  compounds  undergo  changes  in  composition. 
For  example,  the  gypsum  which  is  always  present  in 
acid  phosphates,  liberates  some  potash.     The  potash 
compounds  of  the  soil  are  in  various  degrees  of  com- 
plexity from  forms  soluble  in  dilute  acids  to  insoluble 
minerals  as  feldspar. 

232.  Commercial  Forms  of  Potash.  —  Prior  to  the 


ISO  SOILS   AND    FERTILIZERS 

introduction  of  the  Stassfurt  salts,  wood  ashes  were 
the  main  source  of  potash.  Since  the  discovery  and 
development  of  the  Stassfurt  mines,  the  natural  prod- 
ucts as  kainit,  and  muriate  and  sulphate  of  potash  have 
been  extensively  used  for  fertilizing  purposes.  A 
small  amount  of  potash  is  obtained  also  from  waste 
products  as  tobacco  stems,  cottonseed  hulls,  and  the 
refuse  from  beet-sugar  factories. 

STASSFURT  SALTS 

233.  Occurrence.6*  —  The  Stassfurt  mines  were  first 
worked  with  the  view  of  procuring  rock  salt.     The 
various   compounds   of    potash,   soda  and   magnesia, 
associated  with  the  layers  of  rock  salt,  were  regarded 
as  troublesome  impurities,  and  attempts  were  made  by 
sinking  new  shafts  to  avoid  them,  but  with  the  result 
of  finding  them  in  greater  abundance.     About  1864 
their  value  as  potash  fertilizer  was  established.     It  is 
supposed  that  at  one  time  the  region  about  the  mines 
was  submerged  and  filled  with  sea-water.     The  tropi- 
cal  climate    of  that  geological   period    caused   rapid 
evaporation,  which  resulted  in  forming  mineral  depos- 
its, the  less  soluble  material  as  lime  sulphate  being 
first  deposited,  then  a  layer  of  rock  salt,  and  finally 
layers  of  potash  and  magnesium  salts  in  the  order  of 
their  solubility. 

234.  Kainit  is  a    mineral    composed    of   potassium 
sulphate,  magnesium    sulphate,  magnesium   chloride 
and  water  of  crystallization.      As  it  comes  from  the 
mine  it  is  mixed  with  gypsum,  salt,  potassium  chlo- 
ride, and  other  bodies.     Kainit  contains  from   12  to 


STASSFURT   SALTS  -        iSl 

12.50  per  cent,  potash,  and  is  one  of  the  most  import- 
ant of  the  Stassfurt  salts.  It  is  extensively  used  as  a 
potash  fertilizer,  and  is  also  mixed  with  other  mater- 
ials and  sold  as  a  commercial  fertilizer.  The  mag- 
nesium chloride  causes  it  to  absorb  water,  and  the 
presence  of  other  compounds  results  in  the  formation 
of  hard  lumps,  whenever  kainit  is  kept  for  a  long 
time.  Kainit  is  soluble  in  water,  and  can  be  used  as 
a  top  dressing  at  the  rate  of  75  to  200  pounds  or  more 
per  acre. 

235.  Muriate  of  Potash.  —  This  material  is  exten- 
sively used  as  a  fertilizer  and  is  valuable  for  general 
garden  and  farm  crops.     It  is  a  manufactured  product 
and  ranges  in  purity  from  60  to  95  per  cent,  of  potas- 
sium chloride,  equivalent  to  from  35  to  60  per  cent,  of 
potash,  the   chief   impurity    being  sodium    chloride. 
Potassium  chloride  is  readily  soluble  and  is  a  quick 
acting  fertilizer.     When    used  in  large  amounts,  mu- 
riate of  potash  and  other  chlorides  may  unfavorably 
affect  the  quality  of   some   crops  as  potatoes,  sugar 
beets  and  tobacco.      Ordinarily,  muriate  of  potash  is 
one  of  the  cheapest  and  most  active  forms  of  potash 
and  can  be  used  as  a  top  dressing  at  the  rate  of  200 
pounds   or  more  per  acre  when   preparing  soils  for 
crops.     It  is  valuable  for  grass  and   grain  crops,  and 
has  given  good  results  on  pasty  lands.93 

236.  Sulphate   of   Potash.  —  High-grade   sulphate 
of  potash  is  prepared  from  some  of  the  crude  Stassfurt 
salts,  and  may  contain  as  high  as  97  per  cent.  K2SO  . 
Low-grade  sulphate  of  potash   is  about   90  per  cent, 
pure.     High-grade  sulphate  of  potash  contains  about 


182  SOILS   AND    FERTILIZERS 

50  per  cent,  of  potassium  oxide  (K2O),  and  is  one  of 
the  most  concentrated  forms  of  potash  fertilizer.  It 
is  particularly  valuable  because  it  can  be  safely  used 
on  crops  as  tobocco  and  potatoes  which  would  be  in- 
jured in  quality  if  muriate  of  potash  were  applied,  or 
if  much  chlorine  were  present. 

237.  Miscellaneous  Potash  Salts. —  Carnallit,  9  per 
cent.     K2O,— composed  of  KCl,MgCl2,6H2O.      Poly- 
halit,  15  per  cent.  K2O,— composed  of  K3SO4,MgSO4- 
(CaSO  )2,H2O.     Krugit,  10  per  cent.  K2O, — composed 
of  K2SO4,MgSO4,(CaSO4)4,H2O.      Sylvinit,    16  to  20 
per  cent.  K2O, — composed   of  KCl,NaCl  and  impur- 
ities.      Kieserit,     7    per   cent.    K2O,  — composed   of 
MgSO4  and  carnallit. 

238.  Wood  Ashes.  —  For  ordinary  agricultural  pur- . 
poses,  wood  ashes  are  an  important  source  of  potash. 
Ashes     are    exceedingly    variable     in     composition. 
When  leached  the  soluble   salts   are   extracted    and 
there  is  left  only  about  i  per  cent,  of  potash.      In  un- 
leached  ashes  the  amount  of  potash  ranges  from  2  to 
10  per   cent.     Soft   wood  ashes   contain   much    less 
potash  than  hard  wood  ashes.     Goessmann  gives  the 
following  as  the  average  of  97  samples  of  ashes  :6s 

Average  composition.  Range. 

Per  cent.  Per  cent. 

Potash 5.5  2.5  to  10.2 

Phosphoric  acid 1.9  0.3  to    4.0 

Lime 34.3  18.0  to  50.9 

IN  10,000  POUNDS  OF  WOOD. 

Potash.  Phosphoric  acid. 

Lbs.  Lbs. 

White  oak 10.6  2.5 

Red  oak 14.0  6.0 

Ash 15.0  i.i 

Pine 0.8  0.7 

Georgia  pine 5  .o  1.2 

Dogwood .* 9.0  5.7 


WOOL   ASHES  183 

239.  Action  of  Ashes  on  Soils.  —  Ashes  act  upon 
soils  both  chemically  and  physically.     They  are  usu- 
ally regarded  as  a  potash  fertilizer  only,  but  they  also 
contain  lime  and  phosphoric  acid,  and  may  be  very 
beneficial  in  supplying  these  elements.     The  potash 
is  present  mainly  as  potassium  carbonate.     Ashes  are 
valuable,  too,  because  they  add  alkaline  matter  to  the 
soil,  which  corrects  acidity  and  aids  nitrification.     A 
dressing  of  ashes  improves  the  mechanical  condition 
of  many  soils  by  binding  the  soil  particles.     This 
property  is  well  illustrated  in  the  so-called  "Gumbo" 
soils,  which  contain  so  much  alkaline  matter  that  the 
soil  has  a  soapy  taste  and  appearance,  and  when  plowed 
the  particles  fail  to  separate. 

240.  Leached  Ashes.  —  When  ashes  are  leached  the 
soluble   salts    are  extracted  ;     the    insoluble    matter 
which  is  left  is  composed  mainly  of  calcium  carbonate 
and  silica.66 

Unleached  ashes.  Leached  ashes. 

Per  cent.  Per  cent. 

Water 12.0  30.0 

Silica,  etc 13.0  13.0 

Potassium  carbonate 5.5  i.i 

Calcium                        61.0  51.0 

Phosphoric  acid 1.9  1.4 

241.  Alkalinity  of  Leached  and  Unleached  Ashes. 

— A  good  way  to  detect  leached  ashes  is  to  deter- 
mine the  alkalinity  in  the  following  way  :  Weigh 
out  2  grams  of  ashes  into  a  beaker,  add  100  cc.  dis- 
tilled water,  and  heat  on  a  sand-bath  nearly  to  boiling, 
cool  and  filter.  To  50  cc.  of  the  filtrate  add  about  3 
drops  of  cochineal  indicator,  and  then  a  standard  solu- 


184  SOILS   AND   FERTILIZERS 

tion  of  hydrochloric  acid  from  a  burette  until  the  solu- 
tion is  neutral.  If  a  standard  solution  of  acid  cannot 
be  procured,  one  containing  i5cc.  concentrated  hydro- 
chloric acid  per  liter  of  distilled  water  may  be  used  for 
comparative  purposes.  Leached  ashes  require  less  than 
2  cc.  of  acid  to  neutralize  the  alkaline  matter  in  i  gram 
while  unleached  ashes  require  from  10  to  18  cc.  In  pur- 
chasing wood  ashes,  if  a  chemical  analysis  cannot  be 
secured,  the  alkalinity  of  the  ash  should  be  determined. 

242.  Coal  and  other  Ashes.  —  Since  the  amount  of 
phosphoric  acid  and  potash  in  coal  ashes  is  very  small, 
they  have  but  little  fertilizer  value.     Soft-coal  ashes 
contain  more  potash  than  those  from  hard  coal,  but  it 
is   held    in    such  firm    combination  as  to  be  of   but 
little  value. 

The  ashes  from  sawmills  where  soft  wood  is  burned 
and  the  ashes  are  unprotected,  are  nearly  worthless. 
When  peat-bogs  are  burned  over,  large  amounts  of  ashes 
are  produced.  If  the  bogs  are  covered  with  timber, 
the  ashes  are  sometimes  of  sufficient  value  to  warrant 
their  transportation  and  use. 

Phosphoric 

Potash  acid. 

Per  cent.  Per  cent. 

Hard  coal  ashes o.io  o.  10 

Soft  coal  ashes 0.40  •  0.40 

Sawmill  ashesu 1.20  i.oo 

Peat-bog  ashes1* 1.15  0.54 

Peat-bog  ashes  (timbered)14  3.68  2.56 

Tobacco  stem  ash 4.00  7.00 

Cottonseed  hulls,  ash 20.00  7.00 

243.  Commercial  Value  of  Potash.  —  The   market 
value  of  potash  is  governed  by  the   selling  price  of 


USE    OF   POTASH    FERTILIZERS  185 

high-grade  sulphate  of  potash  and  kainit.  Ordinarily, 
the  price  per  pound  of  potash  varies  from  4  to  5  cents. 
As  in  the  case  of  nitrogen  and  phosphoric  acid,  the 
market  and  field  values  as  determined  by  crop  yields 
may  be  entirely  at  variance.  Before  potash  salts  are 
.used,  careful  field  tests  should  be  made  to  determine 
the  actual  condition  of  the  soil  as  to  its  need  of  potash. 
(See  chapter  X,  Commercial  Fertilizers.) 

244.  Use  of  Potash  Fertilizers.  —  Wood  ashes  or 
Stassfurt  salts  should  not  be  used  in  excessive  amounts. 
Not  more  than  300  pounds  per  acre  should  be  applied 
unless  the  soil  is  known  to  be  markedly  deficient  in 
potash,  and  previous  tests  indicate  that  larger  amounts 
are  safe  and  advisable.     Potash  fertilizers  should  be 
evenly  spread  and  not  allowed  to  come  in  direct  con- 
tact with  plant  roots.     They  should  be  used  early  in 
the  spring  before  seeding  or  before  the  crop  has  made 
much  growth.     Wood   ashes  make  an  excellent  top 
dressing  for  grass  lands,   particularly  where  it  is  de- 
sired  to  encourage  the  growth  of  clover.     There  are 
but  few  crops  or  soils  that  are  not  greatly  benefited  by 
a  light  application  of  wood  ashes,  and  none  should 
ever  be  allowed  to  leach  or  waste  about  a  farm. 

245.  Joint  Use  of  Lime  and  Potash. — When  a  pot- 
ash fertilizer  is  used,  a  dressing  of  lime  will  frequently 
be  beneficial.  The  potash  undergoes  fixation,  and  when 
it  is  liberated  there  should  be  some  basic  material  as 
lime  to  take  its  place.     Goessmann  observed  that  land 
manured    for   several  years  with   potassium    chloride 
finally  produced  sickly  crops,  but  that  an  application 


l86  SOILS   AND   FERTILIZERS 

of  slaked  lime  restored  a  healthy  appearance  to  suc- 
ceeding crops.67  If  the  soil  is  well  stocked  with  lime 
its  joint  use  with  potash  fertilizers  is  not  necessary ; 
if  it  is  acid,  lime  should  be  used  to  correct  the  acidity 
before  the  potash  is  applied.  The  use  of  potash  fer- 
tilizers for  special  crops  is  discussed  in  Chapter  10. 


CHAPTER  IX. 


LIME  AND  MISCELLANEOUS  FERTILIZERS 

246.    Calcium  an  Essential  Element  of  Plant  Food. 

—  Calcium  is  present  in  the  ash  of  all  plants,  and  is 
usually  more  abundant  in  soils  than  phosphorus  or 
potassium.  It  takes  an  essential 
part  in  plant  growth,  and  when- 
ever withheld  growth  is  checked. 
The  effect  of  withholding  cal- 
cium is  shown  in  the  illustration 
(Fig.  33),  which  gives  the  total 
growth  made  by  an  oat  plant 
under  such  a  condition. 

Plants  grown  on  soils  deficient 
in  calcium  compounds,  lack  hard- 
iness. They  are  not  so  able  to 
withstand  drought  or  unfavorable 
climatic  conditions,  as  plants 
grown  on  soils  well  supplied  with 
this  element.  Calcium  does  not 
accumulate  in  the  seeds  of  plants, 
but  is  present  mainly  in  the  leaves 
and  stems  where  it  takes  an  im- 

Oat  pla,!tSgrown  with-    POrtallt     Part     in    the     Production 

out  calcium.  of  new  tissue.     The  term   lime, 

used  in  connection  with  crops  and  soils  refers  to  their 
content  of  calcium  oxid. 


188  SOILS   AND    FERTILIZERS 

247.  Amount  of  Lime  Removed  in  Crops.38 — 

Pounds  per  acre. 

Wheat,  20  bushels i 

Straw,  2000  pounds 7 

Total 8 

Corn,  65  bushels i 

Stalks,  3000  pounds i  [ 

Total 12 

Peas,  30  bushels 4 

Straw,  3500  pounds •  •  •   71 

Total 75 

Flax,  15  bushels 3 

Straw,  1800  pounds . 13 

Total 16 

Clover,  4000  pounds 75 

Clover  and  peas  remove  so  much  lime  from  the  soil 
that  they  are  often  called  lime  plants.  The  amount 
required  by  grain  and  hay  is  small  compared  with  that 
required  by  a  clover  or  pea  crop. 

248.  Amount  of  Lime  in  Soils.  —  There  is  no  other 
element  in  the  soil   in  such   variable  amounts  as  cal- 
cium.    It  may  be  present  from  a  few  hundredths  of  a 
per  cent,   to  twrenty  per  cent,  or  more.     Soils   which 
contain  from  0.4  to  0.5  per  cent,  of  lime  as  carbonate 
are  usually  well  supplied.     The  lime  in  a  soil   takes 
an    important  part    in   soil  fertility ;  when   deficient, 
humic  acid  may  be  formed,  nitrification  checked,  and 
the  soil  particles  will  lack  binding  material. 

249.  Different  Kinds  of  Lime  Fertilizers.  —  By  the 

term    'lime  fertilizer'    is    usually  meant   land  plaster 
(CaSO4,2H2O).      Occasionally  quicklime    (CaO)   and 


LIME   FERTILIZERS  189 

slaked  lime  (Ca  [OH]  2)  are  used  on  very  sour  land.  In 
general  a  lime  fertilizer  is  one  which  supplies  the 
element  calcium ;  common  usage,  however,  has  re- 
stricted the  term  to  sulphate  of  lime. 

250.  Action  of  Lime  Fertilizers  upon  Soils.  —  Lime 
fertilizers  act  both  chemically  and  physically.     Chem- 
ically, lime  unites  with  the  organic  matter  to  form 
humate  of  lime  and  thus  prevents  the  formation  of 
humic  acid.     It  aids  in   nitrification   and"  acts  upon 
the  soil,  liberating  potassium  and  other  elements  of 
plant    food.      Physically,    lime    improves    capillarity, 
precipitates  clay  when  suspended  in  water,  and  pre- 
vents losses,  as  the  washing  away  of  fine  earth. 

251 .  Action  of  Lime  upon  Organic  Matter.  —  When 
soils  are  deficient  in  lime,  an  acid  condition  may  de- 
velop to  such  an  extent  as  to  be  injurious  to  vegeta- 
tion.    Nitrogen,  phosphoric  acid,  and  potash  may  all 
be  present  in  liberal  amounts,  but  in  the  absence  of 
lime  poor  results  will   be  obtained.     Experiments  by 
Wheeler  at  the  Rhode  Island  Experiment  Station  in- 
dicate that  there  are  large  areas  of  acid  soils  in  the 
Eastern  States  which  are  much  improved  when  treat- 
ed with  air-slaked  lime.68     There  is  great  difference 
in  the  power  of  plants  to  live  in   acid  soils.     Some 
agricultural  crops  as  legumes  are  particularly  sensi- 
tive,  while  many  weeds  have  such  strong  power  of 
endurance  that  they  are  able  to  thrive  in  the  presence 
of   acids.      Weeds    frequently    reflect    the    character 
of  a  soil  as  to  acidity,  in  the  same  way  that  an  "alkali" 
soil  is  indicated  by  the  plants  produced. 


SOILS    AND    FERTILIZERS 

252.  Lime  Liberates  Potash.  —  The  action  of  lime 
upon  soils  well  stocked  with  potash  results  in  the  fixa- 
tion of  the  lime  and  the  liberation  of  the  potash;  the 
reaction   takes  place  in  accord  with   the  well-known 
exchange  of  bases   as  explained   in  the  chapter  on 
fixation.     The  extent  to  which  potash  may  be  liber- 
ated by  lime  depends  upon   the  firmness  of  chemical 
combination   with   which   the  potash  is  held   in  the 
soil.       Boussingault    found    that   when    clover    was 
limed  there   was  present  in  the  crop  three  times  as 
much  potash  as  in  a  similar  crop  not  limed.      His  re- 
sults are  as  follows  :69 

Kilos  per  hectare. 

In  crop  not  litned.  In  limed  crop. 

First  Second  First  Second 

year.  year.  year.  year. 

Lime 32.2  32.2  79.4  102.8 

Potash 26.7  28.6  95.6  97.2 

Phosphoric  acid •   n.o  7.0  24.2  22.9 

The  indirect  action  of  land  plaster  upon  Western 
prairie  soils  in  liberating  plant  food,  particularly 
potash  and  phosphoric  acid,  is  unusually  marked. 
Laboratory  experiments  show  that  small  amounts  of 
gypsum  are  quite  active  in  rendering  potash,  phos- 
phoric acid,  and  even  nitrogen  soluble  in  the  soil 
water.5  Occasionally  applications  of  superphosphate 
fertilizers  give  large  yields  due  to  the  gypsum  which 
they  contain,  and  not  to  the  phosphorus. 

253.  Quicklime  and  Slaked  Lime.  —  When  it  is  de- 
sired   to    correct    acidity  slaked   lime  is  used.     Air- 
slacked  lime  is  not  as  valuable   as  water-slaked  lime. 
Quicklime  cannot  be  used  on  land  after  a  crop  has 


LIME    FERTILIZERS  IQI 

been  seeded.  Both  slaked  lime  and  quicklime 
should  be  applied  some  little  time  before  seeding 
and  not  to  the  crop.  Tne  action  of  quicklime  upon 
organic  matter  is  so  rapid  that  it  destroys  vegetation. 
Slaked  lime  is  less  injurious  to  vegetation. 

254.  Pulverized  Lime  Rock.  —  In  some  localities 
pulverized  lime  rock  is  used.     It  may  be  applied  as  a 
top-dressing  in  almost  unlimited  amounts.     It  is  most 
beneficial  on  light,  sandy  soils,  where  it  performs  the 
function  of  fine  clay  as  well  as  being  beneficial  in  its 
chemical  action.     It  is  also  beneficial   on   acid  sods. 
Not  all  soils  are  alike  responsive  to  applications  of 
limestone,  and  before  using,  it  is  best  to  determine 
to  what  extent  it  will  be  beneficial.     There  are  no 
conditions  where  limestone  is  injurious  to  soil  or  crop, 
and  it  is  frequently  very  beneficial. 

255.  Marl.  —  Underlying  beds  of  peat,  deposits  of 
marl  are  occasionally  found.     Marl   is  a  mixture  of 
disintegrated  limestone  and  clay,  and  contains  varia- 
ble amounts  of  calcium  carbonate,  phosphoric  acid, 
and  potash.     When  peat  and  marl  are  found  together 
they  may  be  used  jointly  with  manure  as  described  in 
Section  169.  Many  sandy  lands  in  the  vicinity  of  peat 
and  marl  deposits  would  be  greatly  improved,  both 
physically  and  chemically,  by  the  use  of  these  materials. 

256.  Physical  Action  of  Lime  .—  The  addition  of 
lime  fertilizers  to  sandy  soils  improves  their  general 
physical  condition.     Heavy  clays  lose  their  plasticity 
when   limed  ;    the  fine   clay    particles  are  cemented 
and    act    as   sand,  which    improves    the    mechanical 


IQ2  SOILS    AND    FERTILIZERS 

condition  of  the  soil.  The  physical  action  of  lime 
in  soils  is  well  illustrated  in  the  case  of  'loess  soils/ 
which  are  composed  of  clay  and  limestone.  The  lime 
cements  the  clay  particles  and  forms  compound  grains, 
making  the  soil  more  permeable,  and  more  easily 
tilled.  The  improved  physical  condition  alone  which 
follows  the  application  of  lime  fertilizers,  is  frequently 
sufficient  to  warrant  their  use. 

257.  Application  of   Lime  Fertilizers,  —  Lime  is 
generally  used  as  a  top-dressing  on  grass  lands  at  the 
rate  of  200  to  500  pounds  per  acre.     Excessive  appli- 
cations are  undesirable.     Lime  as  gypsum  is  particu- 
larly valuable  when  applied  to  land  where  crops  are 
grown   which  assimilate   large  amounts  of  lime.     It 
should  be  remembered  that  it  is  not  a  complete  ferti- 
lizer but  simply  an  amendment  and  an  indirect  ferti- 
lizer.10        If  used  to  excess  it  may  get  the  soil  in  such 
condition  that  plant  food  is  not  easily  rendered  avail- 
able.    A  common  saying  is  "  Lime  makes  the  father 
rich  but  the  son  poor."21    This  is  true,  however,  only 
when  lime  is  used  in  excess.     When  used  occasion- 
ally in  connection  with  other  manures,  it  has  no  injur- 
ious effect  upon  the  soil  and  is  a  valuable  fertilizer, 
especially  where  clover  is  grown  with  difficulty. 

MISCELLANEOUS  FERTILIZERS 

258.  Salt  is  frequently  used  as  an  indirect  fertilizer. 
Sodium  and  chlorine,  the  two  elements  of  which  it  is 
composed,  are  not  absolutely  necessary   for   normal 
plant  growth.     When  salt  is  applied  to  the  soil  and 
the  sodium  undergoes  fixation,  potassium  may  be  lib- 
erated.    An  early  experiment  of  Wolff  illustrates  this 


MISCELLANEOUS   FERTILIZERS  193 

point :  a  buckwheat  plot  fertilized  with  salt  produced 
a  crop  with  more  potash  and  less  sodium  than  a  sim- 
ilar unfertilized  plot. 

Salt  may  be  used  to  check  the  rank  growth  of  straw 
during  a  rainy  season,  and  thus  prevent  loss  of  the 
crop  by  lodging.  It  should  not  be  used  in  excessive 
amounts,  as  it  is  destructive  to  vegetation;  200  pounds 
per  acre  is  a  fair  application.  Salt  also  improves  the 
physical  condition  of  the  soil  by  increasing  the  surface- 
tension  of  the  soil  water.  It  should  not  be  used  on  a 
tobacco  or  potato  crop,  because  it  injures  the  quality 
of  the  product.  Salt  is  beneficial  in  preventing  some 
forms  of  fungus  diseases  from  becoming  established 
in  soils. 

259.  Magnesium  Salts. —  Magnesium  is  present  in 
the  ash  of  all  plants,  and  is  an  essential  element  of 
plant  growth.     Usually  soils  are  so  well  stocked  with 
this  element  that  it  is  not  necessary  to  apply  it  in  fer- 
tilizers. Some  of  the  magnesium  salts,  as  the  chloride, 
are  injurious  to  vegetation,  but  when  associated  with 
lime    as    carbonate,    magnesia    imparts    fertility.     In 
many  of  the  Stassfurt  salts  magnesium  is  present. 

260.  Salt.  —  The  deposits  formed  in  boiler  flues  and 
chimneys  when  wood  and  soft  coal  are  burned  contain 
small  amounts  of  potash  and  phosphoric  acid.     Soot 
is  valuable  mainly  as  a  mechanical  fertilizer  and   is 
slow  in  decomposing.     There  is  but  little  plant  food 
in  soot,  as  shown  by  the  following  analysis: 

Soft  coal  soot.  Hard  wood  soot. 

Percent.14  Per  cent. 70 

Potash 0.84  1.78 

Phosphoric  acid 0.75  0.96 

('3) 


194  SOILS   AND   FERTILIZERS 

261.  Seaweeds.  —  Seaweeds  are  rich  in  potash  and 
near  the  sea  coast  are  extensively  used  for  fertilizer. 

Composition  of 

mixed  seaweeds. 

Per  cent.™ 

Water 81.50 

Nitrogen o.  73 

Potash i  .50 

Phosphoric  acid o.  18 

262.  Strand  Plant  Ash.  —  Weeds  and  plants  pro- 
duced on  waste  land  along  the  sea  are  in  many  Euro- 
pean countries  burned  and  the  ashes  used  as  fertilizer 
on  other  lands.     By  this  means  waste  land  is  made  to 
produce  fertilizer  for  fields  which  are  tillable.     The 
amount  of  fertility  removed  in  weeds  is  usually  greater 
than  that  in  agricultural  plants,  because  weeds  have 
greater  power  of  obtaining  food  from  the  soil.     When 
wheat  or  other  grain  is  raised,  and  a  small  crop  of 
grain  and  a  large  crop  of  weeds  are  the  result,  there 
is  more  fertility  removed  from  the  soil  than  if  a  heavy 
stand  of  grain  had  been  obtained.     The  ashes  of  strand 
plants  and  weeds  are  extremely  variable  in  composi- 
tion. 

263.  Wool  Washings  and  Waste — The  washings 
from   wool    contain  sufficient    potash  to  make  them 
valuable    as    fertilizer.     In   wool    there    is    a    high 
per  cent,  of  potash,  which  is  soluble,  and  readily  re- 
moved  in   the  washings.     Wool   waste   may  contain 
from   i   to  5  per  cent,  of  potash  and  from  4  to  7  per 
cent,  of  nitrogen  in  somewhat  inert  forms. 

264.  Street  Sweepings.  —  The  horse  manure  and 
debris  collected  from  paved  streets  in  cities  and  known 


MISCELLANEOUS   FERTILIZERS  195 

as  street  sweepings  have  some  value  as  fertilizer,  and 
are  occasionally  used  for  market  gardening  purposes. 
Street  sweepings,  because  of  the  loss  of  the  liquid  ex- 
crements, have  a  lower  value  than  average  stable 
manure.  They  cannot  be  used  economically  when 
labor  and  the  cost  of  hauling  are  high-priced,  or  when 
a  quick-acting  manure  is  desired.  For  sanitary  rea- 
sons, the  use  of  street  sweepings  is  not  always  desir- 
able, as  mixed  with  the  horse  droppings  frequently 
there  are  associated  accumulations  of  filth  from  dwell- 
ings contaminated  with  disease  producing  germs. 
Crude  garbage  has  a  low  manurial  value,  but  when 
sorted  and  cremated,  the  burned  residue  can  be  used 
to  better  advantage  as  a  fertilizer  than  the  raw  gar- 
bage, and  is  without  the  objectionable  and  unsanitary 
features. 


CHAPTER  X 

COMMERCIAL  FERTILIZERS  AND  THEIR  USE 

265.  Development  of    the    Commercial  Fertilizer 
Industry.  —  The  commercial  fertilizer  industry  owes 
its  origin   to   L,eibig's  work  on  plant  ash.      The  first 
superphosphate  was  made  by  Sir  J.  B.  Lawes,  about 
1840,  from  spent  bone  black  and  sulphuric  acid.     His 
interest  had  previously  been  attracted  to  the  use  of 
bones  by  a  gentleman   who  farmed  near  him,   "  who 
pointed  out  that  on  one  farm  bone  was  invaluable  for 
the  turnip  crop,  and  on  another  farm  it  was  useless."44 
Since   1860  the  commercial  fertilizer  industry  in  this 
country  has  developed  rapidly,  until  now  the  amount 
of  money  expended   in  purchasing  commercial   ferti- 
lizers  and    amendments  is  estimated  at  $60,000,000 
annually.     Nearly  all  of  this  sum  is  expended  in  less 
than  a  quarter  of  the  area  of  the  United  States. 

266.  Complete  Fertilizers  and  Amendments.  —  The 
term  commercial  fertilizer  is  applied  to  those  materials 
made   by  mixing  different  substances  which  contain 
plant  food  in  concentrated  forms.     When  a  commer- 
cial fertilizer  contains  nitrogen,  phosphoric  acid,  and 
potash,  it  is  called  a   complete  fertilizer,  because  it 
supplies    the   three   elements   which   are  most  liable 
to  be  deficient.      Materials  as  sodium  nitrate  which 
supply   only   one    element    are   called  amendments. 
It  frequently  happens  that   a  soil   requires  only  one 
element   in   order  to  produce  good   crops.      In  such 


COMMERCIAL   FERTILIZERS  1 97 

cases  only  the  one  element  needed  should  be  supplied. 
Complete  fertilizers  are  sometimes  used  when  the 
soil  is  only  in  need  of  an  amendment. 

267.  Variable  Composition  of  Commercial  Ferti- 
lizers. —  Since  commercial  fertilizers  are  made  by  mix- 
ing various  materials  which  contain  different  amounts 
of  nitrogen,  phosphoric   acid,  and   potash,   it   follows 
that   they  are  extremely  variable  in  composition  and 
value.      No  two  samples  are  the  same,  hence  the  im- 
portance of  knowing  the  composition  of  every  separate 
brand  purchased.     The  composition  of  fertilizers  is 
varied  to  meet  the  requirements  of  different  soils  and 
crops.      Some  fertilizers  are  made  rich  in  phosphoric 
acid,  while  others  are  rich  in  nitrogen  and  potash. 

268.  How  a  Fertilizer  is  Made. — The  most  com- 
mon  materials  used  in   making  complete  fertilizers 
are  :    Nitrate  of  soda,  kainit,  and  dissolved  phosphate 
rock.     These  materials  have  about  the  following  com- 
position : 

Nitrate  of  soda 15.5  per  cent,  nitrogen. 

Kainit 12.5  per  cent,  potash. 

Dissolved  phosphate  •  •  •    14.0  per  cent,  phosphoric  acid. 

The  fertilizer  may  be  made  rich  or  poor  in  any  one 
element.  Many  fertilizers  contain  about  twice  as 
much  potash  as  nitrogen  and  five  times  as  much  phos- 
phoric acid  as  potash.  In  order  to  make  a  ton  of  such 
a  fertilizer  it  would  be  necessary  to  take  : 

Pounds. 

Nitrate  of  soda 225 

Kainit 425 

Phosphate   1350 


198  SOILS   AND   FERTILIZERS 

The  ton  of  fertilizer  would  then  contain  about  35 
pounds  of  nitrogen,  189  pounds  of  phosphoric  acid 
and  53  pounds  potash.  These  amounts  are  deter- 
mined by  multiplying  the  percentage  composition  by 
the  weight  of  material  taken : 

Pounds. 

Nitrogen 225X0.155=    34.9 

Potash 425*  X  o.  125  =  53.  i 

Phosphoric  acid 135°  X  °- 14    =  189.0 

The  fertilizer  would  then  contain  approximately  1.75 
per  cent,  nitrogen,  2.65  per  cent,  potash,  and  9.45  per 
cent,  phosphoric  acid.  The  percentage  amounts  are 
obtained  by  dividing  the  total  pounds  by  20.  This 
fertilizer,  if  made  at  home  from  materials  purchased 
in  the  market,  would  cost,  exclusive  of  transportation 
and  mixing,  $18.79. 

Pounds.  Cost. 

Nitrogen 34.9  @  14^  cents  =  $5.06 

Phosphoric  acid 189.0  @    6      cents  =11.34 

Potash 53.1  @    4l/2  cents  =    2.39 

Total    $18.79 

A  more  concentrated  fertilizer  could  be  prepared  by 
using  high-grade  sulphate  of  potash,  superphosphate, 
and  ammonium  sulphate.  A  fertilizer  composed  of 
these  ingredients  would  contain  : 


111 

Total  %  6'S 

Pounds.  Percent.      pounds.  Value.    PL,  8«£ 

300  Sulphate  of  ammonia  20  N  60  @  14^  cents  =  $8.70  3.00 
500  Sulphate  of  potash. .  50  K2O  250  @  4^  cents  =11.25  12.50 
1200  Superphosphate 35  P2O5  420©  6  cents  =  25.20  21.00 

Total    $45.15 


COMMERCIAL   FERTILIZERS  199 

So  concentrated  a  fertilizer  as  the  preceeding  is 
rarely,  if  ever,  found  on  the  market,  although  the 
price,  $45.15  per  ton,  is  frequently  charged.  This 
example  is  given  to  show  the  composition  and  cost 
of  one  of  the  most  concentrated  fertilizers  that  can 
be  produced. 

Any  one  of  the  different  materials  mentioned  in  the 
chapters  on  special  fertilizers  could  be  used  in  making 
commercial  fertilizers,  as  dried  blood,  tankage,  nitrate 
of  soda,  sulphate  of  ammonia,  raw  bone,  dissolved 
bone,  raw  phosphate  rock,  dissolved  phosphate  rock, 
basic  slag,  kainit,  muriate  or  sulphate  of  potash,  and 
many  others.  Inasmuch  as  each  of  these  materials 
has  a  different  value,  it  follows  that  fertilizers,  even 
of  the  same  general  composition,  may  have  widely 
different  crop-producing  powers. 

269.  Inert  Forms  of  Plant  Food  in  Fertilizers. — 

A  fertilizer  of  the  same  general  composition  as  the  first 
example  could  be  made  from  feldspar  rock,  apatite 
rock,  and  leather.  The  leather  contains  nitrogen, 
the  apatite  contains  phosphoric  acid,  and  the  feldspar 
potash.  Such  a  fertilizer  would  have  no  value  when 
used  on  a  crop,  because  all  of  the  plant  food  elements 
are  present  in  unavailable  forms.  Hence,  in  purchas- 
ing fertilizers,  it  is  necessary  to  know  not  only  the 
percentage  composition,  but  also  the  nature  of  the 
materials  from  which  the  fertilizer  was  made.  Inert 
forms  of  plant  food  are  akin  to  indigestible  forms  of 
animal  food ;  in  each  it  is  the  part  which  is  assimi- 
lated that  is  of  value. 


200  SOILS   AND   FERTILIZERS 

270.  Inspection   of  Fertilizers. — In   many    states 
laws  have  been  enacted  regulating  the  manufacture 
and   sale  of  commercial  fertilizers,   and  provision  is 
made  for  inspection  and  analysis  of  all  brands  offered 
for  sale.     The  label  on  the  fertilizer  package  must 
specify  the  percentage  amounts  of  available  nitrogen, 
phosphoric    acid    and    potash.     Inspection    has   been 
found  necessary  in  order  to  protect  the  farmer  and  the 
honest  manufacturer.     As  the  result  of  inspection  and 
analysis  occasionally  a  fraud  is  revealed  like  the  fol- 
lowing : 7I 

Natural  plant  food,  $25  to  $28  per  ton. 
Composition.  Per  cent. 

Total  phosphoric  acid 22.21 

Insoluble     "           "    20.81 

Available     "          "     1.40 

Potash  soluble  in  water. 0.13 

Actual  value  per  ton,  $1.52.      . 

271.  Mechanical  Condition  of  Fertilizers. — When 
a   fertilizer    is   purchased,   its    mechanical    condition 
should  be  considered.     The  finer  the  fertilizer,  as  a 
rule,    the   better   it   is  for    promoting    crop    growth. 
Some    combinations   of   plant   food    produce    fertili- 
zers which  become  so  hard  and  lumpy  that  it  is  diffi- 
cult  to   crush    the    lumps    before    spreading.     The 
mass  must  be  pulverized  so  that  it  may  be  evenly  dis- 
tributed, otherwise  the  plant  food  will  not  be  econom- 
ically  used.     A  fertilizer  that  passes  through  a  sieve 
with  holes  0.25  mm.  in  diameter  is  more  valuable  and 
can  be  used  to  better  advantage  than  one  of  the  same 
composition  with  particles  0.5  mm.  in  size. 

272.  Forms  of  Nitrogen  in  Commercial  Fertilizers, 


COMMERCIAL  FERTILIZERS  2OI 

—Nitrogen  is  present  in  commercial  fertilizers  in 
three  forms  :  (i)  Ammonium  salts,  (2)  nitrates,  and 
(3)  organic  nitrogen.  The  organic  nitrogen  is  divided 
into  two  classes  :  (a)  available,  and  (£)  unavailable. 
Pepsin  and  also  potassiu  mpermanganate  are  used  as 
solvents  for  determining  the  availability  of  the  organic 
nitrogen.  The  relative  values  of  the  different  forms 
of  nitrogen  are  discussed  in  Chapter  IV.  Three  fer- 
tilizers may  have  the  same  amount  of  total  nitrogen 
and  still  have  entirely  different  crop-producing  powers. 

No.  i.  No.  2.  No.  3. 

Nitrogen  as  :  Percent.  Percent.  Percent. 

Ammonium  compounds-...    1.75  0.25  o.io 

Nitrates. 0.15  0.15  o.io 

Organic  nitrogen  : 

Soluble  in  pepsin o.io  1.25  0.55 

Insoluble  in  pepsin 0.35  1.25 

Total 2.00  2.00  2.00 

In  purchasing  fertilizers  it  is  important  to  know  not 
only  the  amount  of  nitrogen,  but  also  the  form  in 
which  it  is  present.  In  No.  3  the  nitrogen  is  in  an 
inert  form  like  leather,  while  in  No.  2  it  is  largely  in 
the  form  of  dried  blood,  and  No.  i  has  mainly  am- 
monium compounds.  Each  of  these  fertilizers,  as  ex- 
plained in  the  chapter  on  nitrogenous  manures,  has  a 
different  plant  food  value. 

273.  Phosphoric  Acid. — There  are  three  forms  of 
phosphoric  acid  in  commercial  fertilizers :  (i)  Water 
soluble,  (2)  citrate-soluble,  and  (3)  insoluble.  The 
water  and  citrate-soluble  are  called  the  available  phos- 
phoric acid.  In  most  fertilizers  the  phosphoric  acid 


202  SOILS   AND    FERTILIZERS 

is  derived  from  dissolved  phosphate  rock,  and  is  in  the 
form  of  monocalcium  phosphate.  The  citrate-soluble 
is  mainly  dicalcium  phosphate  with  variable  amounts 
of  iron  and  aluminum  phosphates  in  easily  soluble 
forms.  The  insoluble  phosphoric  acid  is  tricalcium 
and  other  phosphates  which  are  soluble  only  in  strong 
mineral  acids.  The  insoluble  phosphoric  acid  in  fer- 
tilizers is  considered  as  having  but  little  value.  As  in 
the  case  of  nitrogen  three  fertilizers  may  have  the 
same  total  amount  of  phosphoric  acid  and  yet  have 
entirely  different  values. 

No.  i.      No.  2.      No.  3. 
Per  cent.    Per  cent.    Per  cent. 

Water-soluble  phosphoric  acid.     8.00  0.25  0.25 

Citrate-soluble          "  "        1.50  8.00  0.75 

Insoluble  0.50  1.75  9.00 


Total   10.00          10.00          10.00 

No.  3  is  of  but  little  value  ;  the  fertilizer  contains 
insoluble  phosphate  rock  or  some  matarial  of  the  same 
nature.  No  i  is  the  most  valuable,  because  it  con- 
tains dissolved  phosphate  rock  or  dissolved  bone  and 
but  little  insoluble  phosphoric  acid.  No.  2  is  com- 
posed of  such  materials  as  the  best  grade  of  basic  slag 
or  roasted  aluminum  phosphate  or  fine  steamed  bone. 

274.  Potash. — The  three  forms  of  potash  in  fer- 
tilizers are:  (i)  water-soluble,  (2)  acid-soluble,  and  (3) 
insoluble.  Sulphate  of  potash,  kainit,  and  muriate  of 
potash,  are  soluble  in  water  and  belong  to  the  first 
class.  In  some  states  the  fertilizer  laws  recognize 
only  the  water-soluble  potash.  In  the  second  class 
are  found  materials  like  tobacco  stems  and  other 


COMMERCIAL  FERTILIZERS  203 

organic  forms  of  potash.  Substances  like  feldspar, 
which  contain  insoluble  potash,  are  of  no  value  in  fer- 
tilizers. As  a  rule,  the  potash  in  commercial  ferti- 
lizers is  soluble  in  water  ;  in  only  a  few  cases  are  acid- 
soluble  forms  met  with.  Insoluble  potash  would  be 
considered  an  adulterant. 

275.  Misleading  Statements   on  Fertilizer   Pack- 
ages.— Occasionally  the  percentage  amounts  of  nitro- 
gen,  phosphoric  acid,  and  potash  are  stated  in  mis- 
leading ways  ;  as  ammonia,  sulphate  of  potash,  and 
bone  phosphate  of  lime.     Inasmuch  as  ammonia  con- 
tains 14  parts  nitrogen  and  three  parts  by  weight  of 
hydrogen,  it  follows  that  the  ammonia  content  is  pro- 
portionally  greater   than    the  nitrogen   content,    be- 
cause of  the  additional  hydrogen  carried  by  the  ammo- 
nia.    And  so  with  sulphate  of  potash  which  contains 
about  50  per  cent,  potash  and  50  per  cent,  of  sulphuric 
anhydrid.     This  method    of  stating  the  composition 
can  be  considered  in  no  other  way  than  as  a  fraud, 
especially  when  the  fertilizer  contains  no  sulphate  of 
potash,  but  cheaper  materials,  and  the  phosphoric  acid 
is  not  derived  from  bone. 

276.  Estimated  Commercial  Value  of  Fertilizers. 
—  The  estimated  value  of  a  commercial  fertilizer  is 
obtained  from    the   percentage  composition   and   the 
trade  value  of  the  materials  used.     Suppose  that  two 
fertilizers  are  selling  at  $25  and   $30,   respectively, 
each  having  a  different  composition,  the   estimated 
values  of  each  would  be  obtained  in  the  following 
way : 


204 


SOILS   AND   FERTILIZERS 


COMPOSITION  OF  FERTILIZERS. 

No.  i. 

Selling  price  $25. 
Per  cent. 

Nitrogen  as  nitrates 1.50 

Phosphoric  acid,  available 8.00 

"  "      insoluble 2.00 

Potash  (water-soluble) 2.00 

POUNDS  PER  TON. 

No.  i. 

Nitrogen i  .50  X  20  =    30 

Phosphoric  acid  •  •  8.0    X  20  —  !6o 
Potash 2.0   X2o=    40 

ESTIMATED  VALUE. 

No.  i. 

Nitrogen 30  X  0.145  =  $4-35 

Phosphoric  acid 160  X  °-o6   =    9.60 

Potash 40X0.045—    i. 80 


NO.   2. 

Selling  price  $30. 
Per  cent. 

2.IO 

IO.OO 

0.50 
3-50 


No.  2. 

2.IOX  20  —  42 
IO.O  X  2O  =  2OO 
3.5  X  20=  70 


No.  2. 


42  Xo.i45  =  $6-°9 
200  X  0.06  =12.00 
70X0.045=   3.15 


$15-75 

Difference    between    estimated    value    and 
price,  No.  i,  $9.25;  No.  2,  $8.76. 


$21.24 
selling 


Fig.  34.     Composition  of  Fertilizers. 

277.  Home  Mixing  of   Fertilizers. — At  the  New 

Jersey  Experiment  Station  it  has  been  shown  that 
"  the  charges  of  the  manufacturers  and  dealers  for 
mixing,  bagging,  shipping,  and  other  expenses  are  on 
the  average  $8.50  per  ton,  and  also  that  the  average 
manufactured  fertilizer  contains  about  300  pounds  of 


COMMERCIAL  FERTILIZERS  205 

actual  fertilizing  constituents  per  ton.  These  figures 
are  practically  true  of  other  states  where  large  quan- 
tities of  commercial  fertilizers  are  used."72  In  states 
where  smaller  amounts  are  used  the  difference  between 
the  estimated  cost  and  selling  price  is  greater  than 
P-50. 

These  facts  emphasize  the  economy  of  home  mix- 
ing. The  difference  in  price  between  the  raw  mate- 
rials and  the  product  sold  is  frequently  so  great  that 
it  is  an  advantage  for  the  farmer  to  purchase  the  raw 
materials,  as  sulphate  of  potash,  nitrate  of  soda,  and 

•8 

gj 

fS  if 

a'5  N 
FORMULA  No.  i.  g  &3 

Pounds.                                                          Pounds.  £  g£ 

Nitrate  of  soda 500    containing  nitrogen 77.5  3.87 

Acid  phosphate 1200    containing  phos.  acid...    168.0  8.40 

Sulphate  of  potash ..     300    containing  potash 150.0  7.50 


Total 395.5 

FORMULA  No.  2. 

Nitrate  of  soda 250     containing  nitrogen 38.7       1.99 

Acid  phosphate 900     containing  phos.  acid...  126.0       6.3 

Sulphate  of  potash . .     450    containing  potash 225.0     11.5 

Plaster,  etc 400 

Total 389.7 

FORMULA  No.  3. 

Nitrate  of  soda 200    containing  nitrogen 31.0       1.55 

Acid  phosphate 1500     containing  phos.  acid...  210.0     10.50 

Sulphate  of  potash  . .     150    containing  potash 75.0      5.75 

Plaster,  etc 150 

Total 316.0 


206  SOILS   AND    FERTILIZERS 

acid  phosphate,  and  mix  them  as  desired.  By  so 
doing  a  fertilizers  of  any  composition  may  be  pre- 
pared and  there  is  less  danger  of  securing  an  inferior 
article.  Of  course  it  is  not  possible  by  means  of 
shovels  and  sieves  to  accomplish  as  thorough  mixing 
of  the  ingredients  as  with  machinery. 

278.  Fertilizers    and     Tillage. — Commercial     fer- 
tilizers cannot  be  made  to  take  the  place  of  good  till- 
age, which  is  equally  as  important  when  fertilizers 
are  used  as  when  they  are  omitted.     Scant  crops  are 
as  frequently  due  to  the  want  of  proper  tillage  as  to 
the  absence  of  plant  food.     Poor  cultivation  results  in 
getting  the  soil  out  of  condition  ;  then  instead  of  thor- 
ougly  preparing  the  land,  commercial  fertilizers  are 
resorted  to,  and  the  conclusion  is  reached  that  the  soil 
is   exhausted,   when  in  reality  it  is  suffering  for  the 
want  of  cultivation,  for  a  dressing  of  land  plaster,  for 
farm  manures,  or  for  a  change  of  crops.     There  is  no 
question   but  what  better  tillage,  better  care  and  use 
of  farm  manures,  the  culture  of  clover  and  the  sys- 
tematic rotation  of  crops  would  result  in  greatly  re- 
ducing  the  amount  annually  spent   for  commercial 
fertilizers,  and  also  increasing  the  yield  of  crops.     The 
better  the  cultivation,  the  less  the  amount  of  commer- 
cial fertilizer  required.     Cultivation  cannot,  however, 
entirely  take  the  place  of  fertilizers. 

279.  Abuse  of  Commercial   Fertilizers. — When  a 
soil  produces  poor  crops,  a  complete  fertilizer  is  fre- 
quently   used    when  an  amendment   only  is  needed. 
Restricted  crop  production  in  long  cultivated  soils  is 


COMMERCIAL  FERTILIZERS  207 

usually  due  to  deficiency  of  humus  and  available 
nitrogen.  If  the  nitrogen  were  supplied,  improved 
cultivation  together  with  the  chemical  action  of  the 
humus  on  the  soil  would  generally  furnish  the  avail- 
able potash  and  phosphoric  acid,  but  instead  of  pro- 
viding the  one  element  needed,  others  which  may 
already  be  present  in  the  soil  in  liberal  amounts,  are 
often  supplied  at  an  unnecessary  expense.  Another 
abuse  of  fertilizers  is  their  application  to  the  wrong 
crop.  A  heavy  application  of  potash  fertilizer  to  a 
wheat  crop  grown  on  a  clay  soil,  or  an  application  of 
nitrate  of  soda  on  land  seeded  to  clover,  or  of  land 
plaster  to  flax  grown  on  a  limestone  soil,  would  be 
a  waste  of  money. 

280.  Judicious  Use  of  Fertilizers. — In  order  to 
make  the  best  use  of  commercial  fertilizers,  both 
the  soil  and  the  crop  must  be  carefully  considered. 
All  crops  do  not  possess  the  same  power  of  assimilat- 
ing food  ;  turnips,  for  example,  have  very  restricted 
powers  of  phosphate  assimilation,  hence  they  require 
phosphate  manures.  Wheat  requires  help  in  obtain- 
ing its  nitrogen.  In  some  soils  a  wheat  crop  may 
starve  for  want  of  nitrogen,  while  an  adjoining  corn 
crop  will  scarcely  feel  its  need.  Wheat  has  strong 
power  of  assimilating  potash,  while  clover  has  less. 
Hence  in  the  use  of  fertilizers  the  power  of  the  plant 
to  obtain  its  food  must  be  considered.  A  light  appli- 
cation of  either  a  special  purpose  or  a  complete  fertili- 
zer at  the  time  of  seeding  is  often  advantageous,  as 
it  encourages  plant  growth  by  supplying  food  at  the 


208  SOILS   AND   FERTILIZERS 

time  when  it  is  most  needed.  There  should  be  some 
plant  food  in  the  soil  in  a  highly  available  condition 
for  the  use  of  young  plants,  after  that  stored  up  in  the 
seed  has  been  exhausted.  Before  commercial  fertilizers 
are  used,  careful  field  trials  should  be  made. 

281.  Experimental   Plots.— A  piece  of  land  well 
tilled  and  of  uniform  texture,  should  be  used  for  field 
trials  with  fertilizers.     After  preparation  for  the  crop, 
small  plots,   1/20  of  an  'acre,  are  staked  off.     A  con- 
venient size  is,  length  204  feet,  width  lofeet  8  inches, 
area  2176  square  feet.     Between  each  plot  a  strip  3 
feet  wide  is  left.     The  plan  is  to  apply  one  element 
or  a  combination   of  elements  to  a  plot  and   compare 
the  results  with  other  plots  treated  differently.70 

282.  Preliminary  Trials.  — It  is  best  to  make  pre- 
liminary trials  one  year  and  verify  the  conclusions  the 
next.     In  making  the  tests  the  first  year  eight  plots 
are  necessary  and  fertilizers  are  applied  in  the  follow- 
ing way : 

The  first  plot  receives  no  fertilizer  and  is  used  as 
the  basis  for  comparison. 

The  second  plot  receives  a  dressing  of  8  pounds 
nitrate  of  soda,  16  pounds  acid  phosphate,  and  8 
pounds  sulphate  or  muriate  of  potash. 

The  third  plot  receives  nitrogen  and  phosphoric 
acid. 

The  fourth  plot  receives  nitrogen  and  potash. 
The  fifth  plot  receives  nitrogen. 


COMMERCIAL  FERTILIZERS 


209 


The  sixth  plot  receives  phosphoric  acid  and  potash. 

The  seventh  plot  receives  potash. 

The  eighth  plot  receives  phosphoric  acid. 


No  fertilizer' 

N 

N 

N 

P205 

P205 

K2O 

K2O 

i. 

2. 

3- 

4- 

N 

P205 

K20 

P205 

K2O 

5- 

6. 

7- 

8. 

Should  good  results  be  obtained  on  plot  No.  3,  the 
indications  are  that  there  is  a  deficiency  of  the  two 
elements  nitrogen  and  phosphoric  acid.  An  increased 
yield  from  No.  4  indicates  deficiency  of  nitrogen  and 
potash.  Under  such  conditions  the  use  of  a  complete 
fertilizer  would  be  unnecessary.  If  No.  5  gives  an 
additional  yield  the  soil  is  in  want  of  nitrogen.  From 
the  eight  plots  it  will  be  possible  to  tell  which  of  the 
various  elements  it  is  advisable  to  use.  The  fertilizers 
should  be  applied  after  the  land  has  been  thoroughly 
prepared  and  before  seeding.  Corn  is  a  good  crop  for 
the  first  trials.  The  number  of  plots  may  be  increased 
by  using  well-prepared  stable  manure  and  gypsum  on 
plots  9  and  10  respectively.  The  second  year  the 
results  should  be  verified. 

283.  Deficiency  of  Nitrogen. — If  the  results  indi- 
cate a  deficiency  of  nitrogen,  select  two  crops,  one  as 
wheat  which  is  particularly  benefited  by  dressings  of 
nitrogen,  and  another  as  corn  which  has  less  difficulty 
in  obtaining  this  element.  The  cultivation  of  each 

(14) 


210  SOILS    AND   FERTILIZERS 

crop  should  be  that  which  experience  has  shown  to 
be  the  best.  On  one  wheat,  and  one  corn  plot,  8 
pounds  of  nitrate  of  soda  should  be  used,  a  plot  each 
of  wheat  and  corn  being  left  unfertilized.  If  both  the 
corn  and  the  wheat  are  benefited  by  the  application 
of  nitrogen,  the  soil  is  in  need  of  available  nitrogen. 
If,  however,  the  wheat  responds  and  the  corn  does  not, 
the  soil  is  not  in  great  need  of  nitrogen  but  does  not 
contain  an  abundance  in  available  forms. 

284.  Deficiency   of  Phosphoric   Acid. — In  experi- 
menting with  phosphoric  acid,  turnips  are  grown  on 
two  plots  and   barley   on   two  plots.     To  one  plot  of 
each    1 6  pounds  of  acid  phosphate   are  applied.     If 
both  crops  show  marked  additional  yields  the  soil  is 
in    need  of   available  phorphoric   acid.     If  only    the 
turnips  respond  while  the  barley  is  indifferent,  the  soil 
contains  a  fair  amount  of  available  phosphoric  acid. 
Barley  and  turnips  are  used   because  there  is  such  a 
marked  difference   in  the  power  of  each  to  assimilate 
phosphoric  acid. 

285.  Deficiency  of  Potash, — In  order  to  determine 
the   condition   of  the  soil   as   to  potash,  potatoes  and 
oats  may   be  used  as  the  trial  crops,  and  8  pounds  of 
sulphate  of  potash  should  be  applied  to  one  plot  of  each. 
Marked  additional  yields  indicate  a  poverty  of  availa- 
ble potash  ;  an  increased  potato   crop  and  an  indiffer- 
ent oat  crop  indicate  potash  not  in  the  most  available 
forms.      If   no    additional   yields    are  obtained   from 
either  crop  the  soil  is  not  in  need  of  potash. 


COMMERCIAL  FERTILIZERS  211 

286.  Deficiency  of  Two  Elements. — If  the  prelim- 
inary trials  indicate  a  deficiency  of  two  elements  as 
nitrogen    and    phosphoric    acid,    in    verifying    these 
results,  both  elements  are  used  together,  in   the  same 
way  as  described  for  deficiency  of  nitrogen,  with  addi- 
tional plots  for  the  separate  application  of  nitrogen 
and  phosphoric  acid. 

287.  Importance  of  Field  Trials. — While  it  is  a 
difficult  matter  to  determine  the  actual   needs  of  a 
soil,   it  will   be  found   that  both  time  and  money  are 
saved  by  a  systematic  study  of  the  question.    Suppose 
fertilizers  are  used  in  a   "hit  or  miss"  way  year  after 
year  on  a  soil,   deficient  only  in  phosphoric  acid.     It 
might   take  8  years  to  indicate  what  the  soil   really 
as  deficient    in    if  a  different  fertilizer  is  used  each 
year,   and    during    all    this    period,  either    the    soil 
fails  to  receive  its  proper  fertilizer,  or  expensive  and 
unnecessary  plant  food  is  provided.      Field  tests  to  be 
of  value  must  be  continued  for  a  number  of  years  and 
the  results  verified. 

288.  Will  it  Pay  to  Use  Commercial  Fertilizers? 

— This  question  can  be  answered  only  by  trial.  If  a 
soil  is  in  need  of  available  plant  food,  the  additional 
yield  of  crops  should  pay  for  the  fertilizer  and 
the  expense  of  using  it.  Some  fertilizers  have  an 
influence  on  two  or  three  succeeding  crops,  and  only 
partial  returns  are  received  the  first  year.  When 
large  crops  must  be  produced  on  small  areas,  as  in 
truck  farming,  commercial  fertilizers  are  generally 
necessary.  In  the  production  of  large  areas  of  staple 


212  SOILS   AND   FERTILIZERS 

crops  as  wheat  and  corn,  in  the  western  prairie  states, 
they  have  tfot  as  yet  been  used.  If  there  is  a  good 
stock  of  natural  fertility,  the  soil  is  well  tilled,  farm 
manures  are  used,  and  crops  systematically  rotated,  the 
use  of  commercial  fertilizers  can  be  avoided.  With 
poor  cultivation  and  a  soil  that  has  been  impover- 
ished by  injudicious  cultivation  their  use  is  more 
necessary.  Commercial  fertilizers  sometimes  fail  to 
give  beneficial  results,  because  of  either  an  excessively 
acid  or  alkaline  condition  of  the  soil. 

289.  Amount  of  Fertilizer  to  Use  per  Acre. — When 
commercial  fertilizers  are  used,  it  should  be  the  aim 
in  general  farming  to  apply  just  enough  to  produce 
normal  yields.     Heavy  applications  at  long  intervals 
are  not  as  productive  of  good  results  as  light  applica- 
tions more  frequently.     From  400  to  600  pounds  per 
acre  is  as  much  as  should  be   used  at  one  time  unless 
previous  trials  have  shown  that  heavier  applications 
are  necessary.     The  way  in  which  the  fertilizer  is  to 
be  applied,  as  broadcast  or  otherwise,   must  be  deter- 
mined by  the  crop  to  be  grown.     The  fertilizer  should 
not  come  in  direct  contact  with  seeds,  neither  should 
it  be  plowed  under  or  worked  into  the  soil  to  such  a 
depth  that  it  may  be  lost  by  leaching  before  it  can  be 
appropriated  by  the  crop. 

290.  Excessive  Applications  of  Fertilizers  Injuri- 
ous.— An  overabundance  of  plant  food  has  an  inju- 
rious effect  upon  crop  growth.     Plants  take  their  food 
from  the  soil  in  dilute  solutions,  and  when   the  solu- 
tion is  concentrated  abnormal  growth  results.     Pota- 


COMMERCIAL  FERTILIZERS  213 

toes  heavily  manured  with  nitrate  of  soda  make  a 
luxuriant  growth  of  vines  but  produce  only  a  few 
small  tubers.  When  a  medium  dressing  is  used  along 
with  potash  and  phosphoric  acid,  a  more  balanced 
growth  is  obtained,  and  a  better  yield  is  the  result. 

Heavy  applications  of  nitrate  of  soda  produce  a  rank 
growth  of  straw,  with  a  low  yield  of  grain.  The  ex- 
cessive amount  of  nitrogen  causes  the  mineral  matter 
to  be  utilized  for  straw  production  and  leaves  only  a 
small  amount  for  grain  production.  When  applica- 
tions of  commercial  fertilizers  aro  too  heavy,  plants 
take  up  unnecessary  amounts  of  food  and  fail  to  make 
good  use  of  it.  In  fact  crops  may  be  overfed  or  fed, 
an  unbalanced  ration,  the  same  as  animals.  Hence 
in  the  use  of  fertilizers  excessive  or  unbalanced  appli- 
cations are  to  be  avoided. 

291.  Fertilizing  Special  Crops. — There  are  crops 
which  need  special  help  in  obtaining  some  one  ele- 
ment, and  in  the  use  of  fertilizers  it  should  be  the 
rule  to  help  those  crops  which  have  the  greatest  diffi- 
culty in  obtaining  food.  When  the  soil  does  not  show 
a  marked  deficiency  in  any  one  element,  light  dress- 
ings of  special  purpose  manures  may  be  made  to  the 
following  crops  : 

Wheat. — Nitrogen  first,  then  phosphoric  acid. 

Barley,  oats,  and  rye  require  manuring  like  wheat, 
but  to  a  less  extent.  Each  crop  has  a  different  power 
of  obtaining  nitrogen.  Wheat  requires  the  most  help 
and  barley  and  rye  the  least. 


214  SOILS   AND   FERTILIZERS 

Corn. — Phosphoric  acid  first,  then  nitrogen  and 
potash. 

Potatoes. — General  manuring,  re-enforced  with  pot- 
ash. 

Ma  ngels. — N  i  tr  ogen . 

Turnips.— Phosphoric  acid. 

Clover. — Lime  and  potash. 

Timothy. — General  manuring. 

292. — Commercial  Fertilizers  and  Farm  Manures. 
— Commercial  fertilizers  should  not  replace  farm 
manures,  but  simply  re-enforce  them.  Although 
commercial  fertilizers  are  called  complete  manures, 
they  fail  to  supply  organic  matter.  It  is  more  im- 
portant in  some  soils  than  in  others,  that  the  organic 
matter  be  maintained,  because  in  some  soils  the 
organic  matter  takes  a  more  important  part  in  crop 
production  than  does  the  food  applied  in  commercial 
forms.  When  a  rich  prairie  soil  is  reduced  by  grain 
cropping  and  is  allowed  to  return  to  pasture,  heavier 
yields  of  grain  are  afterwards  obtained  than  from  sim- 
ilar soils  which  have  received  only  applications  of  com- 
mercial fertilizers.  This  is  due  to  the  action  of  the 
humus  in  the  soil.  At  the  Canadian  Dominion  Ex- 
perimental farms  where  comparative  trials  have  been 
made  for  fourteen  years  with  farm  manures  and  com- 
mercial fertilizers,  it  has  been  found  that  farm 
manures  even  on  new  lands  give  better  results  than 
commercial  fertilizers  for  production  of  wheat  and 
corn.  » 


CHAPTER  XI 

FOOD  REQUIREMENTS  OF  CROPS 

293.  Amount  of  Fertility  Removed  by  Crops.— 

From  an  acre  of  soil,  producing  average  crops,  the 
amount  of  fertility  removed  varies  between  wide  lim- 
its. For  example,  an  acre  of  mangels  removes  150 
pounds  of  potash,  while  an  acre  of  flax  removes  27 
pounds  ;  an  acre  of  corn  removes  about  75  pounds 
of  nitrogen,  while  an  acre  of  wheat  removes  35 
pounds.  Crops  which  remove  the  most  fertility  do 
not  always  require  the  most  help  in  obtaining  their 
food.  This  is  because  the  amount  of  plant  food 
assimilated  is  not  a  measure  of  the  power  of  crops 
to  obtain  food.  An  acre  of  corn,  for  example,  takes 
over  twice  as  much  nitrogen  as  an  acre  of  wheat,  but 
wheat  will  often  leave  the  soil  in  a  more  impover- 
ished condition  than  corn,  because  corn  has  greater 
power  for  procuring  nitrogen  and  for  utilizing  that 
formed  by  nitrification  after  the  wheat  crop  has  com- 
pleted its  growth.  The  available  nitrogen  if  not 
utilized  by  a  crop  may  be  lost  in  various  ways.  Man- 
gels require  about  twice  as  much  phosphoric  acid  as 
flax,  but  are  a  strong  feeding  crop  and  require  less 
help  in  obtaining  this  element. 

It  was  formerly  believed  that  the  plant  food 
present  in  the  matured  crop  indicated  the  kind 
and  amount  of  fertilizing  ingredients  to  apply,  and 
that  a  correct  system  of  manuring  required  a  return 


2l6 


SOILS   AND    FERTILIZERS 


to  the  soil  of  all  elements  removed   in  the  crop.     Ex- 
periments   have    shown    that  this  view  is  incorrect. 
The   composition  of  plants  cannot   be   taken  as  the 
PI^ANT  FOOD  REMOVED  BY  CROPS37 


Pounds  per  acre. 
Phos- 

Gross 

Nitro- 

phoric 

Pot- 

Sil- 

Total 

Crops. 

weight. 

gen. 

acid. 

ash. 

lyime. 

ica. 

ash 

Wheat,  20  bus  

I2OO 

25 

12.5 

7 

I 

I 

25 

Straw  

2000 

IO 

7-5 

28 

7 

115 

185 

Total  

35 

20 

35 

^8 

116 

2IO 

Barley,  40  bus  

I92O 

28 

15 

8 

i 

12 

40 

Straw  

3000 

12 

5 

3° 

8 

60 

I76 

Total  

40 

20 

38 

9 

72 

216 

Oats,  50  bus  

I6OO 

35 

12 

IO 

1-5 

15 

55 

Straw  

3000 

15 

6 

35 

9-5 

60 

150 

Total  

50 

18 

45 

II.  0 

75 

205 

Corn,  65  bus  

2200 

40 

18 

15 

i 

i 

40 

Stalks  

3OOO 

35 

2 

45 

ii 

89 

1  60 

Total  

75 

2O 

60 

12 

90 

200 

Peas,  30  bus  

1800 

.. 

18 

22 

4 

i 

64 

Straw  

3500 

.. 

7 

38 

71 

9 

176 

Total  

25 

60 

75 

10 

240 

Mangels,  lotons.. 

2OOOO 

75 

35 

150 

3° 

10 

350 

Meadow  hay,  i  ton 

2OOO 

3° 

20 

45 

12 

50 

175 

Red    Clover    Hay, 

2  tons  

4OOO 

.. 

28 

66 

75 

15 

250 

Potatoes,  150  bus.. 

9000 

40 

20 

75 

25 

4 

125 

Flax,  15  bus  

9OO 

39 

15 

8 

3 

05 

34 

Straw  

1800 

15 

3 

J9 

13 

3 

53 

Total  

54 

18 

27 

16 

3-5 

87 

basis  for  their  manuring.  For  example  an  acre  of 
wheat  contains  35  pounds  of  nitrogen  while  an  acre 
of  clover  contains  70  pounds.  If  70  pounds  of  nitro- 
gen were  applied  to  an  acre  of  clover  and  35  pounds 
to  an  acre  of  wheat,  poor  results  would  follow,  be- 
cause clover  can  obtain  its  own  nitrogen  while  wheat 


FOOD  REQUIREMENTS  OF  CROPS  217 

is  nearly  helpless  in  obtaining  it,  and  the  35  pounds 
would  not  necessarily  come  in  contact  with  the  roots 
so  that  it  could  all  be  assimilated.  While  the  amount 
of  plant  food  removed  in  crops  cannot  serve  as  the 
basis  for  their  manuring,  valuable  results  are  ob- 
tained from  a  study  of  the  different  elements  of  fer- 
tility removed  in  crops.  In  making  use  of  the  pre- 
ceding table,  other  factors,  as  the  influence  of  the 
crop  upon  the  soil  and  the  power  of  the  crop  to  ob- 
tain its  food,  must  also  be  considered. 

294.  Plants  Exert  a  Solvent  Power  in  Obtaining 
Food.  —  It  was  supposed  at  one  time  that  plants  ob- 
tained all  of  their  mineral  food  from  the  mineral  matter 
dissolved  in  the  soil  water.  See  Section  87.  Experiments 
by  L,iebig  demonstrated  that  plants  have  the  power  of 
rendering  a  large  portion  of  their  own  food  soluble, 
provided  it  does  not  exist  in  forms  too  inert  to  under- 
go chemical  change.  Liebig  grew  barley  in  boxes  so 
constructed  that  all  of  the  water-soluble  plant  food 
could  be  secured.  Two  of  the  boxes  were  manured 
and  two  left  unmanured.  In  one  box  which  received 
manure  and  one  which  received  none,  barley  was 
grown.  One  each  of  the  manured  and  unmanured 
boxes  was  left  barren.  He  collected  all  of  the  drain 
waters  and  determined  the  soluble  mineral  matter 
present,  also  weighed  and  analyzed  the  crops.  His 
results  showed  that  92  per  cent,  of  the  potash  in  the 
crop  was  obtained  from  forms  insoluble  in  water.73 
Other  experiments  have  shown  that  the  leachings 
from  a  fertile  soil  do  not  contain  sufficient  plant  food 
to  grow  a  normal  crop.87 


2l8  SOILS   AND    FERTILIZERS 

In  the  roots  of  all  plants  there  are  present  various 
organic  acids  and  salts.  Between  the  rootlet  and  the 
soil  there  is  a  layer  of  water.  The  plant  sap  and  the 
soil  water  are  separated  by  plant  tissue  which  serves  as 
a  membrane.  All  of  the  conditions  are  favorable  for 
osmosis.  The  sap  from  the  roots  finds  its  way  into 
the  soil  in  exchange  for  some  of  the  soil  water.  The 
acid  and  compounds,  excreted  by  the  roots,  act  upon 
the  mineral  matter,  rendering  portions  of  it  soluble, 
when  it  is  taken  up  by  the  plant.  Different  plants  con- 
tain different  kinds  and  amounts  of  solvents,  as  well 
as  present  different  areas  of  root  surface  to  act  upon 
.the  soil,  and  the  result  is  that  agricultural  crops  have 
different  powers  of  assimilating  food.  This  action  of 
living  plant  roots  upon  soils  is  a  digestion  process  which 
is  somewhat  akin  to  the  digestion  of  food  by  animals. 

Plants  not  only  possess  the  power  of  rendering  their 
food  soluble  but  they  are  also  able  to  select  their  food 
and  to  reject  that  which  is  unnecessary.  For  ex- 
ample, wheat  grown  on  prairie  soil  containing  soda  in 
equally  abundant  and  soluble  forms  as  the  potash, 
will  contain  relatively  little  soda  compared  with  the 
potash.37 

CEREAL  CROPS 

295.  General  Food  Requirements. — Cereal  crops  con- 
tain a  high  per  cent,  of  silica  and  evidently  possess 
the  power  of  feeding  upon  some  of  the  simpler  silicates 
of  the  soil74  liberating  the  base  elements  and  using 
them  as  food,  while  the  silica  is  deposited  in  the 
outer  surface  of  the  straw.  As  previously  stated, 


FERTILIZERS  FOR  CEREAL  CROPS  2  19 

cereal  crops,  although  they  do  not  remove  large 
amounts  of  total  nitrogen  from  the  soil,  require 
special  help  in  obtaining  this  element.  There  is, 
however,  a  great  difference  among  the  cereals  as  to 
power  of  assimilating  nitrogen.  Next  to  nitrogen 
these  crops  stand  most  in  need  of  phosphoric  acid. 
The  humic  phosphates  are  utilized  by  nearly  all  of 
the  cereals. 

296.  Wheat.  —  This  crop  is  more  exacting  in  its 
food  requirements  than  barley,  oats,  or  rye.  Wheat 
is  comparatively  a  weak  feeding  crop,  and  the  soil 
should  be  in  a  higher  state  of  fertility  than  for  other 
grains.  The  extensive  experiments  of  L,awes  and 
Gilbert  have  given  valuable  information  regarding 
the  effects  of  manures  on  wheat.  Their  results  are 
given  in  the  following  table  :  74 

AVERAGE  YIELD  OF  WHEAT  PER  ACRE. 

Bushels. 
No  manure  for  40  years  ........................    14 

Minerals  alone  for  32  years  .....................    15^ 

Nitrogen      "       "    "      "     .....................    23.1 

Farmyard  manure  for  32  years  ..................    32f 

Minerals  and  nitrogen  for  32  years1  .............  36^ 


1  86  pounds  of  nitrogen  as  sodium  nitrate. 

2  86        "        "          "         "  ammonium  salts. 


The  food  requirements  of  wheat  are  such  that  it 
should  be  given  a  favored  position  in  the  rotation.  It 
may  follow  clover  provided  the  clover  sod  is  light 
and  is  fall  plowed.  On  some  soils,  however,  wheat 
does  not  thrive  following  a  sod  crop,  as  it  takes  nearly 
a  year  for  a  heavy  sod  residue  to  get  into  suitable  food 


220  SOILS   AND   FERTILIZERS 

forms  for  a  wheat  crop.  Under  such  a  condition,  oats 
should  first  be  sown,  then  wheat  may  follow.  On 
average  soil  a  medium  clover  sod,  plowed  late  in 
summer  or  in  early  fall,  and  followed  by  surface  cul- 
tivation, leaves  the  land  in  good  condition  for  spring 
wheat.  It  is  not  advisable  to  have  wheat  follow  bar- 
ley, because  the  soil  will  be  too  porous,  and  barley 
being  a  stronger  feeding  crop  leaves  the  land  in  poor 
condition  as  to  available  plant  food.  When  a  corn 
crop  is  well  manured,  wheat  may  follow.  The  food 
requirements  of  wheat  are  best  satisfied  following 
a  light,  well  cultivated  clover  sod,  or  following  oats, 
which  have  been  grown  on  heavy  sod,  or  following 
corn  that  has  been  well  manured.  When  wheat  is 
judiciously  grown  in  a  rotation  and  farm  manures  are 
used  it  is  not  an  exhausting  crop. 

297.  Barley. — While  wheat  and  barley  belong  to 
the  same  general  class  of  cereals,  they  differ  greatly 
in  their  habits  and  food  requirements.  Barley  is  a 
stronger  feeding  crop,  has  greater  root  development 
near  the  surface,  and  can  utilize  food  in  cruder  forms. 
In  many  of  the  western  states,  soils  which  produce 
poor  wheat  crops,  from  too  long  cultivation,  give  ex- 
cellent yields  of  barley.  This  is  due  to  changed  con- 
ditions, of  both  the  chemical  and  mechanical  composi- 
tion of  the  soil.  Long  cultivation  has  made  the  soil 
porous  and  reduced  the  nitrogen  content.  Barley 
thrives  best  on  a  rather  open  soil  and  has  greater 
nitrogen  assimilative  powers  than  wheat.  Barley, 
however,  responds  liberally  to  manuring,  particularly 


FERTILIZERS  FOR  CEREAL   CROPS  221 

to  nitrogenous  manures.  The  experiments  of  Lawes 
and  Gilbert  on  the  growth  of  barley  are  briefly  sum- 
marized in  the  following  table.75 

AVERAGE  YIELD  OF  BARLEY  PER  ACRE  FOR  34  YEARS. 

Bushels. 

No  manure 17! 

Superphosphate  alone 23^ 

Mixed  minerals 24^ 

Nitrogen  alone 3o| 

Nitrogen  and  superphosphate 45 

Farmyard  manures ....  49*- 

298.  Oats. — Oats  are  capable  of  obtaining  food  un- 
der more  adverse   conditions    than  either   barley  or 
wheat.     They  are  also  less  exacting  as  to  the  physical 
condition  of  the  soil.     The  oat  plant  will  adapt  itself 
to  either  sandy  or  clay  soil,  and  will  thrive  in  the 
presence  of   alkaline   matter   or   humic   acid   where 
wheat  would  be  destroyed.     In  a  rotation,  oats  usually 
occupy  a  position  less  favored  by  manures.     Oats  are, 
however,  greatly  benefited  by  fertilizers  particularly 
by  those  of  a  nitrogenous  nature. 

299.  Corn. — Experiments  with  corn  indicate  that 
under  ordinary  conditions  it  requires  most  help  in  ob- 
taining phosphoric  acid.     Corn  removes  a  large  amount 
of  gross  fertility  but  its  habits  of  growth  are  such  that 
it  generally  leaves  an  average  soil  in  better  condition 
for  succeeding  crops.     Corn  is  not  injured  as  are  many 
grain  crops  by  heavy  applications  of  stable  manure. 
It  does  not,  like  flax,  produce  waste  products  which 
are   destructive   to   itself.     Rich   prairie   soils  when 
newly  broken  give  better  results  for  wheat  culture 


222  SOILS   AND   FERTILIZERS 

after  one  or  two  corn  crops  have  been  removed.  The 
food  requirements  of  corn  are  satisfied  by  applications 
of  stable  manure,  occasionally  re-enforced  with  a  little 
nitrogen  and  phosphoric  acid.  After  clover,  corn  gives 
excellent  returns,  and  when  corn  is  the  chief  market 
crop  it  should  be  favored  by  having  the  best  position 
in  a  rotation. 

MISCELLANEOUS  CROPS 

300.  Flax  is  very  exacting  in  food  requirements 
and  for  its  culture  the  soil  must  be  in  a  high  state  of 
fertility.  It  is  a  type  of  weak  feeding  crop.  There  are 
but  few  roots  near  the  surface  and  consequently  it 
has  restricted  powers  of  nitrogen  assimilation.38  Flax 
should  be  indirectly  manured.  Direct  applications  of 
stable  manure  produce  poor  results,  but  when  the 
manure  is  applied  to  the  preceding  crop  excellent  re- 
sults are  obtained.  Flax  does  not  remove  a  large 
amount  of  fertility,  but  if  grown  too  frequently  the 
tendency  is  to  get  the  land  out  of  condition  rather 
than  to  exhaust  it.  The  best  conditions  for  flax  cul- 
ture require  that  it  should  be  grown  on  the  same  land 
only  once  in  five  years.  Flax  straw  does  not  form 
suitable  manure  for  flax  lands.  Dr.  Lugger  has 
demonstrated  that  there  are  produced,  when  the  roots 
and  straw  of  flax  decay,  products  which  are  destruc- 
tive to  succeeding  flax  crops.77  Flax  diseases  are  also 
introduced  into  land  by  the  use  of  diseased  flax  seed. 
The  food  requirements  of  flax  are  met  when  it  follows 
corn  which  has  been  well  manured,  or  a  sod  which 
has  been  given  the  cultivation  described  for  wheat. 


FERTILIZERS   FOR    ROOT   CROPS  223 

Flax  and  spring  wheat  are  much  alike  in  food  require- 
ments. 

301.  Potatoes.* — Potatoes  are  surface  feeders  and 
when  grown  continually  upon  the  same  soil  without 
manure,  the  yield  per  acre  decreases  more  rapidly  than 
that  of  any  other  farm  crop.    Experiments  with  pota- 
toes by  Lawes  and  Gilbert,  using  different  manures, 
gave  the  following  result  : ?8 

AVERAGE  YIELD  PER  ACRE  FOR  12  YEARS. 

Tons.  Cwt. 

No  manure i  19! 

Superphosphate 3  5 

Minerals  alone 3  yf 

Nitrate  of  soda  alone 2  4f 

Mixed  manures  and  nitrogen 5  17! 

Farm  manures,  alternate  years 4  3! 

Potatoes  require  liberal  general  manuring  re-enforced^ 
with  wood  ashes  or  other  potash  fertilizer.  In  the 
rotation  they  should  follow  grain  or  pasture  land,  pro- 
vided the  fertility  of  the  soil  is  kept  up. 

302.  Sugar-Beets.  —  This  crop  is  more  exacting  in 
its  food  requirements  than  any  other  root  crop.     Ex- 
cessive fertility  is  not  conducive  to  a  high  content  of 
sugar.     Soils   in   a  medium   state  of  fertility  usually 
give  the  best  results.79  Sugar-beets  should  not  receive 
heavy  dressings  of  stable  manure,   because  an    abnor- 
mal growth  results.     Nitrogenous  fertilizers  can  be 
applied  only  in  limited  amounts,  heavier  dressings  of 
potash    and    phosphoric    acid    are    more    admissible. 
When  sugar-beets  follow  corn  which  has  been  manured, 
or  grain  which  has  left  the  soil  in  an  .average  state  of 
fertility,  the  food  requirements  are  well  met. 


224  SOILS   AND   FERTILIZERS 

303.  Roots.  —  Mangels  are    gross    feeders  and  re- 
move a  larger  amount  of  fertility  from  the  soil  than 
any  other  farm  crop.74      When  fed  -to   stock   and  the 
manure  is  returned  to  the  soil  they  materially  aid  in 
making  the  plant  food  more  available  for    delicate 
feeding  crops.     Mangels  are  better  able  to  obtain  their 
phosphoric  acid  than  are  turnips  and  need  the  most 
help  in   the  way  of  nitrogen.     Turnips  are  surface 
feeders  with  stronger  power  of  nitrogen   assimilation 
than  the  grains,  but  with   restricted   power  of  phos- 
phate assimilation.     Manures  for  turnips  should  be 
phosphatic  in  nature. 

304.  Rape  is  a  type  of  strong  feeding  plant  capa- 
ble of  obtaining  its  food  under  conditions  adverse  to 
grain  crops.     When  grown  too  frequently  upon  the 
same  soil  it  does  not  thrive.     On  account  of  its  great 
capacity  for  obtaining  food,  it  is  a   valuble  crop  to 
use  for  green  manuring  purposes.80 

305.  Buckwheat  is  a  strong  feeding   crop  and  its 
demands  for  food  are  easily  met.     On  rich  soil,  a  rank 
growth  of  straw  results,    with   poor  seed  formation. 
Buckwheat  is  usually  sown  upon  the  poorest  soil  of 
the  farm.     Being  a   strong   feeder   it   is    used    as   a 
manurial  crop,  being  plowed    under   while  green  to 
serve  as  food  for  weaker  feeding  crops. 

306.  Cotton.  —  On  average  soils  cotton  stands  in 
need  first  of  phosphoric  acid,  second  of  nitrogen.81     It 
is  most  able  to  obtain   potash.     Organic  nitrogen  as 
cottonseed  meal  and   stable  manure  appear   equally 
as  effective  as  nitric  nitrogen.     Phosphoric  acid  must 


FERTILIZERS   FOR   GRASS   CROPS  225 

be  applied  in  the  most  available  forms.  In  fertilizing 
cotton,  the  use  of  green  manuring  crops  as  cow  peas 
with  an  application  of  marl  gives  beneficial  results. 
Marl,  which  is  composed  mainly  of  calcium  carbonate, 
combines  with  the  acids  formed  from  the  decay  of 
this  vegetable  matter  and  as  a  result  the  plant  food  of 
the  soil  is  more  available,  a  result  which  is  beneficial 
to  both  soil  and  crop.  There  are  but  few  crops  which 
respond  so  readily  to  fertilizers  as  cotton. 

307.  Hops,  —  The  hop  plant  is  exacting  in  regard 
to  its  food  requirements.     An  excess  of  easily  soluble 
plant  food  is  injurious  while  a  lack  is  equally  so.     An 
abundance  of  food  in  organic  forms  is  most  essential. 
Heavy  dressings  of  farm  manures    may    be  applied. 
Where  hops  are  grown  there  is  a  tendency  to  use  all 
of  the  manure  on  the  hops  while  the  rest  of  the  farm 
is  left  untnanured.     Very  light  applications  of   com- 
mercial fertilizers    may  be    used   in  connection  with 
stable   manure,  but  such  use  should   be  made    only 
after  a  preliminary  trial  on  a  small  scale. 

308.  Hay  and  Grass  Crops.  —  Most  grass  crops  have 
shorter  roots  than  grain  crops ;  they  are  surface  feed- 
ers and  not  so  able  to  secure  mineral  food.     When  a 
number  of  crops  have  been  removed  the  soil  may  stand 
in  need  of  available  mineral  matter.     Farm   manures 
are  particularly  well  adapted  for  fertilizing  grass.    Ap- 
plications of  nitrogenous  manures  result  in  discourag- 
ing the  growth  of  clover.     Heavy  manuring  of  grass 
land  has  a  tendency  to  reduce  the  number  of  species 
and  one  kind  is  apt  to  predominate.82     On  some  soils 

('5) 


226  SOILS   AND   FERTILIZERS 

ashes,  and  on  others  lime  fertilizers,  have  been  found 
very  beneficial.  The  manuring  of  grass  lands  must 
be  varied  to  meet  the  requirements  of  different  soils. 
Permanent  meadows  require  different  manuring  from 
meadow  introduced  as  an  important  crop  in  the  rota- 
tion. Permanent  meadows  should  receive  an  annual 
dressing  of  farm  manure  or  of  a  commercial  fertilizer 
containing  phosphoric  acid,  potash  and  a  fair  amount 
of  nitrogen. 

309.  Leguminous    Crops. — For  leguminous  crops 
potash  and  lime  fertilizers  have  been  found  of  most 
value.      Analyses   of    clover   and   peas,   show    large 
amounts    of    both    potash    and    lime.     Some    crops 
as    clover    fail    when    grown    too    frequently    upon 
the  same  soil,  not  because  the  soil  is  exhausted  but  be- 
cause of  the  development  in   the  soil  of  organic  pro- 
ducts which  are  destructive  to  growth.     As  the  result 
of  growing  leguminous   crops  and  after  their  inex- 
pensive  food    requirements  are  met,   the  soil  is  en- 
riched   with    nitrogen    and    the   phosphoric   acid    is 
changed  to  available  forms. 

310.  Garden  Crops.  —  For  general  garden  purposes, 
there  should  be  a  liberal  supply  of  plant  food.     Well 
composted  farm  manure  can  advantageously  be  rein- 
forced with  commercial  fertilizers.     A  liberal   use  of 
manures  insures   not  only  the  maximum  yield,   but 
crops  of  the  best  quality.     Maturity  of  crops  also  is 
influenced  by  fertilizers. 

Voorhees89  recommends  as  a  fertilizer  for  general  gar- 
den purposes  one  containing  : 


FERTILIZERS   FOR   GARDEN   CROPS  227 

Per  cent. 

Nitrogen 4.00 

Phosphoric  acid 8.00 

Potash .   10.00 

This  and  similar  fertilizers  can  be  applied  at  the  rate 
of  looo  pounds  per  acre.  To  meet  the  requirements 
of  special  crops,  as  spinach  and  cabbage,  an  additional 
dressing  of  nitrate  of  soda  may  be  used.  Asparagus 
should  preferably  be  fertilized  after  harvesting  the 
crop  so  as  to  encourage  new  growth  and  the  storing 
up  of  reserved  builing  material  in  the  roots  for  next 
year's  growth. 

For  early  maturing  garden  crops,  a  fair  but  not 
excessive  amount  of  nitrogen  should  be  applied, 
also  a  more  liberal  supply  of  phosphates  will  be 
found  advantageous.  Some  garden  crops,  as  cu- 
cumbers, pumpkins  and  squash  thrive  best  when 
their  food  is  supplied  in  organic  forms,  as  the  humate 
compounds  derived  from  farm  manures.  A  continu- 
ous supply  of  available  plant  food  is  thus  furnished  to 
the  growing  crop.  Onions  are  benefited  by  a  gener- 
ous dressing  of  soluble  nitrogen.  Celery  also  should 
be  well  supplied  with  soluble  nitrogen  combined  with 
soluble  forms  of  mineral  food.  Tomatoes  require 
general  fertilizing ;  for  early  maturity,  nitrogen,  as 
nitrate  of  soda,  is  beneficial,  but  an  excess  should  be 
avoided ;  for  late  maturity,  farm  manures  and  com- 
mercial fertilizers  containing  less  nitrogen  can  be 
used.  For  general  garden  purposes,  a  complete  fertili- 
zer is  preferable  to  an  amendment,  as  a  better  bal- 
anced growth  is  secured  which  favorably  affects  both 
yield  and  the  quality  of  the  crop. 


228  SOILS   AND   FERTILIZERS 

311.  Fruit  Trees. — In  the  manuring  of  fruit  trees,  it 
should  be  the  object  first  to  produce  thrifty  trees  as  sub- 
sequent fertilizing  to  produce  fruit  will  not  give  satis- 
factory results  with  poorly  grown  and  partially  de- 
veloped trees.     In  order  to  promote  growth,  a  liberal 
supply  of  a  complete  fertilizer  should  be  used.     When 
an  orchard  is  in  full  bearing,  there  is  as  heavy  a  draft 
upon  the  soil  as  when  a  wheat  crop  is  grown.?0     To 
meet  this,  farm   manures  and  commercial   fertilizers 
should  be  used  liberally.     The  quality  of  the  fruit  is 
often  adversely  affected  by  a  scant  supply  of  plant 
food.     A   quick    acting    fertilizer   containing  kainit, 
nitrate  of  soda,  and  dissolved  phosphate  rock  should 
be  used  in  the  spring,  followed  if  necessary  by  a  light 
dressing  of  some  manure  which  yields  up  its  fertility 
more  slowly.       Stone  fruits  are  benefited  by  the  addi- 
tion of  lime  to  the  fertilizer. 

312.  Lawns.  —  In  the   preparation   of   a   lawn,   a 
mixture  of  six  parts  of  bone  ash,  two  parts  of  muriate 
of  potash  and  one  part  of  nitrate  of  soda  can  be  ap- 
plied at  the  rate  of  5  to  7  pounds  per  square  rod  prior 
to  seeding.     A  good  lawn  should  have  a  subsoil  that 
is  fairly  retentive  of  moisture,   one  containing   10  to 
15  per  cent,   of  clay  or  a  large  amount  of  fine  silt. 
Too  much  potash  and  lime  encourage  exclusive  growth 
of  clover  and   crowding  out  of  grasses.     During  the 
season,  two  or   three  applications  can  be  made  of  a 
commercial  fertilizer  containing  about  3  per  cent,  of 
nitrogen,  10  per  cent,  of  phosphoric  acid,  and  3  per 
cent,   of  potash,  at  the  rate  of  about  one  pound  per 


MISCELLANEOUS   CROPS  229 

square  rod.  When  part  of  the  nitrogen  is  in  the  form 
of  nitrates  and  part  as  ammonium  salts,  better  results 
are  secured  than  when  the  nitrogen  is  all  in  one  form. 
It  is  also  advisable  to  supply  the  phosphoric  acid  in 
more  than  one  form.  An  even  application  of  fertili- 
zer to  a  lawn  is  quite  necessary,  otherwise  the  growth 
is  "  patchy."  Hard  wood  ashes  evenly  spread  at  the 
rate  of  i  to  2  pounds  per  square  rod  can  also  be  used 
advantageously  as  a  lawn  fertilizer,  and  when  used, 
they  should  be  reinforced  with  nitrate  of  soda. 


CHAPTER  XII 


ROTATION  OF  CROPS  AND  CONSERVATION  OF  SOIL 
FERTILITY 

313.  Object  of  Crop  Rotation.  —  The  object  of 
systematic  rotation  of  crops  is  to  conserve  the  fertility 
of  the  soil,  and  at  the  same  time  to  produce  larger 
yields.  In  order  to  accomplish  this,  the  food  require- 
ments of  different  crops  must  be  met  by  good  culti- 
vation and  judicious  manuring.  Rotations  must  be 
planned  according  to  the  nature  of  the  soil  and  the 
system  of  farming  that  is  to  be  followed.  For  general 
grain  farming  a  different  rotation  is  required  than  for 
exclusive  dairying.  Whatever  the  nature  of  farming 
the  whole  farm  should  gradually  undergo  a  systematic 
rotation.  If  the  farm  is  uneven  in  soil  texture,  differ- 
ent rotations  can  be  practiced  on  the  various  parts. 
There  is  no  way  in  which  soils  are  more  rapidly  de- 
pleted of  fertility  than  by  the  continued  culture  of  one 
crop.  In  exclusive  wheat  raising,  for  example,  the 
losses  which  occur  are  not  confined  to  the  fertility  re- 
moved in  the  crop  but  there  are  other  losses  as  described 
in  the  chapter  on  nitrogen.  When  wheat  is  system- 
atically grown  in  alternation  with  other  crops,  losses 
of  nitrogen  are  reduced  to  a  minimum. 

When  remunerative  crops  can  no  longer  be  produced 
the  soil  is  said  to  be  exhausted.  Soil  exhaustion  may 
be  due  either  to  a  lack  of  fertility  or  to  the  soil  being 
temporarily  out  of  condition  because  of  a  one-crop 
system  and  poor  methods  of  cultivation. 


ROTATION   OF   CROPS  231 

314.  Principles  Involved  in  Crop  Rotation,  —  In 

the  systematic  rotation  of  crops  there  are  a  few  funda- 
mental principles  with  which  all  rotations  should  con- 
form. Briefly  stated  these  principles  are : 

1.  Deep  and  shallow  rooted  crops  should  alternate. 

2.  Humus-consuming  and  humus-producing  crops 
should  alternate. 

3.  Crops  should  be  rotated  so  as  to  make  the  best 
use  of  the  preceding  crop  residue. 

4.  Crops  should  be  rotated  so  as  to  secure  nitrogen 
indirectly  from  atmospheric  sources. 

5.  Crops  should  be  rotated  so  as  to  keep  the  soil  in 
the  best  mechanical  condition. 

6.  In  arid  regions  crops  should  be  rotated  so  as  to 
make  the  best  use  of  the  soil  water. 

7.  An  even  distribution  of  farm  labor  should  be  se- 
cured by  a  rotation. 

8.  Farm  manures  and  fertilizers  should  be  used  in 
the  rotation  where  they  will  do  the  most  good. 

9.  Rotations  should  be  planned  so  as  to  produce 
fodder  for  stock,  and  so  that  every  year  there  will  be 
some  important  crop  to  be  sold. 

315.  Deep   and  Shallow  Rooted  Crops.  —  When 
deep  and  shallow  rooted  crops  alternate,  the  draft  upon 
the  surface  soil  and  subsoil  is  more  evenly  distributed. 
In  many  soils  nitrogen  and  phosphoric  acid  are  more 
abundant  in  the  surface  soil  while  potash  and   lime 
predominate  in  the  subsoil.     When  such  a  condition 
exists,  the   alternating   of  deep   and   shallow  rooted 
crops  is  very  beneficial,  because  the  surface  soil  is  re- 


232  SOILS   AND   FERTILIZERS 

lieved  of  continuous  heavy  drafts  upon  the  elements 
present  in  scant  amounts. 

316,  Humus-consuming     and     Humus-producing 
Crops.  —  When  grain  or  hoed   crops  are  grown  con- 
tinually,   oxidation    of    the  humus  occurs,  and   the 
chemical  and  physical  properties  of  the  soil   may   be 
entirely  changed  by  the  loss  of  the   humus.     The  ro- 
tating of  grass  and  grain  crops  and  the   use   of  stable 
manure  serve  to  maintain  the  humus  equilibrium.  On 
some  soils  lime  may  be  required  along  with  the  humus 
to  prevent  the  formation  of  humic  acid,  and   in   such 
cases  the  best  conditions  exist  when  both  lime  and  hu- 
mus materials  are  supplied.     The   alternation   of  hu- 
mus-producing and  humus-consuming  crops  is  one  of 
the  essential  matters  to  consider  in  a  rotation. 

317.  Crop  Residues.  —  Crop  residues  should  always 
be  placed  at  the  disposal  of  weak  feeding  crops.     For 
example,  after  a  light  clover  and  timothy-  sod,  wheat 
or  flax  should   be  grown   in  preference  to  barley  or 
mangels.     The  weak  feeding  crop  should  then  be  fol- 
lowed by  a  strong  feeding  crop,  and  each  is  properly 
supplied  with  food.     It  would  be  poor  economy,  on  an 
average  soil,  to  follow  clover  and  timothy  with  mangels, 
then  with  barley,  and   finally  with  flax,  because  the 
flax  would  be  placed  at  a  serious  disadvantage  follow- 
ing two  strong  feeding  crops.     If  reversed,  the  crops 
would  be  placed  in  order  of  assimilative  power,  and  the 
best   use    would    be  made  of   the    sod  crop  residue. 
When  crops  of  dissimilar  feeding  habits  follow  each 
other  in  rotation  not  only  are  the  crop  residues  used  to 


ROTATION   OF   CROPS  233 

the  best  advantage,  but  the  soil  is  relieved  of  excessive 
demands  on  special  elements.  For  example,  wheat 
and  clover  take  different  amounts  of  potash  and  lime 
from  the  soil.  Wheat  has  the  power  of  feeding  upon 
silicates  of  potash  which  clover  cannot  assimilate, 
hence  wheat  and  clover  in  rotation  relieve  the  soil  of 
excessive  demands  on  the  potash. 

318.  Nitrogen-consuming  and  Nitrogen-producing 
Crops.  —  It  is  possible  in  a  five-course  rotation  to  main- 
tain or  even  increase  the  nitrogen  of  the  soil  without 
the  use  of  nitrogenous  manures.     In  Section  134  an 
example  is  given  of  a  rotation  which  has  left  the  soil 
with  a  better  supply  of  nitrogen   than   at  the  begin- 
ning.    When  a  soil  produces  a  good  clover  crop  once 
in  five  years,  and  stable  manure  is  used  once  during 
the  rotation,  the  soil   nitrogen  is  not  decreased.     By 
means  of  rotating  nitrogen-producing   and    nitrogen- 
consuming   crops   grain    can  be  sold  from  the  farm 
without  purchasing  nitrogenous  manures.     The  con- 
servation of  the  nitrogen  and  the  humus  of  the  soil 
is  one  of  the   most  important  points  to   consider  in 
the  rotation  of  crops. 

319.  Influence  of  Rotation  upon  the  Mechanical 
Condition  of  Soils.  —  With  different  kinds  of  crops, 
the  mechanical  condition  of  soils  is  constantly  under- 
going change.     Grain  crops  and  hoed  crops  tend  to 
make  the  soil  open  in  texture.     Grass  crops  have  the 
opposite   effect.     All   soils  should    undergo   periodic 
compacting  and  loosening.     Some  require  more  of  one 
treatment    than    of    the   other.     In    a    rotation    the 


234  SOILS   AND   FERTILIZERS 

action  of  the  crop  upon  the  mechanical  condition  of 
the  soil  should  be  considered,  otherwise  the  soil  may 
get  into  poor  condition  to  retain  water  or  become  so 
loose  that  heavy  losses  occur  through  wind  storms. 
Sandy  soils  are  improved  by  those  methods  of  cropping 
which  compact  the  soil,  while  heavy  clays  require  the 
opposite  treatment.  The  rotation  should  be  made  to 
conform  to  the  requirements  of  the  soil. 

320.  Economic  Use   of  Soil  Water. — The  rotation 
should  not  be  of  such  a  nature  as  to  make  excessive 
demands  upon  the  soil  water.     For  example,  after  a 
grain  crop  has  been  produced,  it  is  best  in   regions  of 
scant  rainfall  to  plow  the  land  and  get  it  into  condi- 
tion to  conserve  the  water  for  the  next  year's  crop, 
rather  than  to  attempt  to  raise  a  catch  crop  the  same 
year.     During  years  of  heavy  rainfall  catch  crops  can 
be  grown  as  green  manure  to  increase  the  humus  con- 
tent of  the  soil.     Crops  removing  excessive  amounts 
of  water  should  not  be  grown  too  frequently.     Sun- 
flowers, for  example,  remove  twenty  times  more  water 
than  grain  crops.      Cabbage   removes   from    the   soil 
more  water  than  many  other  crops.     With    a   good 
rotation  and  systematic  cultivation  it  is  possible  to 
carry  a  water  balance  in  the  soil  from  one  year  to  the 
next,  so  that  crops  will  be  supplied  in  times  of  drought. 

321.  Rotation  and  Farm  Labor. — The  rotation  of 
crops  should  be  planned  so  that  an  even  distribution 
of  farm  labor  is   secured.     The   importance   of  this 
is  so  plain  that  its  discussion  is  unnecessary.     It  is 
one  of   the  most   important   points   to    consider    in 


ROTATION    OF   CROPS  235 

economic  farming,  and  should  not  be  lost  sight  of  in 
planning  rotations. 

322,  Economic    Use   of   Manures. — Farm  manure 
should  be  applied  to  those  crops  which  experience  has 
shown  to  be  the  most  benefited  by  its  use.     At  least 
once  during  a  five  years'  rotation  the  land  should  receive 
a  dressing  of  stable  or  some  other  manure.     If  com- 
mercial fertilizers  are  used,  they  should  be  applied  to 
the  crops  which  require  the  most  help  in  obtaining 
food.     With   the  growing  of  clover  and  the  use  of 
farm  manures,  only  the  poorer  kinds  of  soil  will  re- 
quire commercial  fertilizers  for  general  crop  produc- 
tion.    It  is  more  economical  to   reenforce  the   farm 
manures  with  fertilizers  especially  adapted  to  the  soil 
and  crop,  than  to  purchase  complete  fertilizers  for  all 
crops. 

323.  Salable   Crops.  —  In  all  farming,  something 
must  be  sold  from  the  farm.     It  should  be  the  aim  to 
sell  products  which  remove  the  least  fertility,  or  if 
those  are  sold  which  remove  large  amounts,  to  return 
in  cheaper  forms  the  fertility  sold.     In  a  good  rotation 
it  is  the  plan  to  have  at  least  one  salable  crop  each 
year.     The  whole  farm  need  not  undergo  the  same 
rotation  at  the  same  time  and  the  rotation  may  be 
subject  to  minor   changes  as   circumstances  require. 
To  illustrate,  wheat  and  flax  occupy  about  the  same 
position  in  a  rotation.     If  at  seeding  time  the  indica- 
tions are  that  wheat  will  be  a  poor  paying  crop  and 
flax   command   a   high    price,  flax  should  be  sown. 
The  rotation  should  be  such  that  one  of  two  or  three 
crops  may  be  grown  as  circumstances  require. 


236  SOILS   AND   FERTILIZERS 

324.  Rotation   Advantageous    in  Other  Ways. — 
A  good  rotation  will  be  found  advantageous  in  other 
ways.     With    one    line    of    cropping,    land    becomes 
foul  with   weeds  and   insects   which    are    unable    to 
thrive  when  crops  are  rotated.      Frequently  the  rota- 
tion must  be  planned  so  as  to  reclaim  the  land  from 
weeds,  and  ravages  caused  by  insect  pests.     Many  in- 
sects are  capable  of  living  only  on   a  special   crop  ; 
w.hen  this  crop  is  grown  continually  on  the  same  land 
the  best  conditions  for  insect  ravages  exist,  and  relief 
is  only  secured  by  rotation  of  crops.     Fungus  diseases 
also  are  most  liable  to  occur  on  soils  which   produce 
annually  the  same  crop,  as  the  conditions  are  favorable 
for  the  propagation  and   hybernating  of  disease  pro- 
ducing spores. 

325.  Long-  and  Short- Course  Rotations.  —  Rota- 
tions vary  in  length  from  2  to  17  years.     Long-course 
rotations  are  more  generally  followed    in   European 
and  other  of  the  older  countries.     The  length  of  the 
rotation  can  only  be  determined  by  the  conditions  ex- 
cisting  in  different  localities.     As  a  general  rule  long- 
course    rotations    should    be    attempted    only  after    a 
careful  study  of  all  of  the  conditions  relating  to  the 
system  of  farming  that  it  is  desired  to  follow.     For 
northern   latitudes   a  rotation   of   four  or  five    years 
gives    excellent    results.       In  some  localities  three- 
course  rotations  are  the  most  desirable. 

A  rotation  that  is  suitable  for  one  locality  or  kind 
of  farming  may  be  unsuitable  for  other  localities  or 
conditions.  Because  of  variations  in  soil,  climate, 


ROTATION   OF   CROPS  237 

and  rainfall,  no  definite  standard  rotation  can  be  pro- 
posed that  will  be  applicable  to  all  conditions. 

326.  Example  of  Rotation. — In  dealing  with  the 
subject  of  rotations  it  is  best  to  take  actual  problems 
as  they  present  themselves  and  plan  rotations  that 
will  best  meet  all  of  the  conditions.  For  example,  a 
farm  of  160  acres  is  to  be  rotated  with  the  main  ob- 
ject of  producing  fodder  for  live  stock,  and  a  small 
amount  of  grain  for  sale.  To  meet  these  require- 
ments the  rotation  outlined  on  pages  238  and  240  is 
given.83 

The  farm  is  divided  into  eight  fields  of  20  acres 
each  ;  seven  fields  are  brought  under  the  rotation, 
while  one  field  is  left  free  for  miscellaneous  purposes. 
Each  year  there  are  produced  20  acres  of  corn,  20 
acres  of  timothy  and  clover  hay,  10  acres  each  of 
wheat  and  flax,  20  acres  of  barley,  and  five  acres  each 
of  corn  fodder,  rye,  peas,  and  potatoes,  while  20  acres 
are  reserved  for  pasture.  The  main  income  is  de- 
rived from  the  sale  of  live  stock  and  dairy  products. 


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240  SOILS   AND   FERTILIZERS 

Problems  on  Rotations 

1.  Plan  a  rotation  for  general  farming  ( 160  acres)   using  the 
following  crops:  clover,  timothy,  barley,  oats,  potatoes,  and  corn. 
The   soil   is  in  an  average  state  of  fertility.     Twenty-five  head  of 
stock  are  kept. 

2.  Plan  a  three-course  rotation  for  a  sandy  soil,  the  main  ob- 
ject being  potato  culture. 

3.  Plan  a  seven-year  rotation  for  grain  farming,  using  manure 
and  a  commercial  fertilizer  once  during  the  rotation.     The  soil  is 
a  clay  loam  in  a  good  state  of  fertility. 

4.  Plan  a  rotation  for  general  farming  on  a  sandy  loam. 

5.  How  would  you  proceed  to  bring  an  old  grain  farm  from  a 
low  to  a  high  state  of  productiveness  ?     Begin  with  the  feeding  of 
the  stock. 

6.  Using  commercial  and  special  purpose  manures,  how  would 
you  proceed  to  raise  wheat,  potatoes,  and  hay,  in  rotation  and  con- 
tinually ? 

7.  Plan  a  rotation  for  a  northern  latitude,  where  corn  cannot 
be  grown,  except  for  fodder,  and  where  clover  and  timothy  fail  to 
do  well  ;    wh^at  and  all   small  grains  thrive,  also  millet,  bromus 
inermis,  rape,  and  some  of  the  root  crops.    The  soil  is  a  clay  loam, 
resting  on  a  marl  subsoil.     Manure  is  very  slow  in  decomposing. 
The  rotation  should  be  suited  to  general  farming,   wheat  or  flax 
being  the  important  market  crop. 

8.  Plan  for  a  southern  farm  a  rotation  in  which  cotton  forms 
an  important  part. 


CONSERVATION  OF  FERTILITY 

327.  Manures  Necessary  for  Conservation  of  Fer- 
tility. —  In  order  to  conserve  the  fertility  of  the  soil, 
not  only  must  a  systematic  rotation  be  practiced,  but 
a  proper  use   must   be  made  of  the  crops  produced. 
When  crops  are  sold  from  the  farm  and  no  restoration 
is  maed,  soils  are  gradually  depleted  of  their  fertility. 
No  soil  has  ever  been  found  that  will  continue  to  pro- 
duce crops  without  the  use  of  manures.     Many  prairie 
soils  give  large  yields  for  long  periods  without  manur- 
ing, but  they  are  never  able  to  compete  in  productive- 
ness with  similar  soils  that  have  been  systematically 
cropped  and  manured.     With  a  fertile  soil  the  decline 
of  fertility  is  so  gradual  that  it  is  not  observed  unless 
careful  records  are  kept  of  the  yields  from  year  to  year. 

328,  Use  of  Crops.  —  The  use  made  of  crops  whether 
as  food  for  stock  or  sold  directly  from  the  farm,  deter- 
mines the  future  crop-producing  power  of  the  soil. 
With  different  systems  of  farming  different  uses  are 
made  of  crops.     When  exclusive  grain  farming  is  fol- 
lowed rio  restoration  of  fertility  is  made,  while  in  the 
case  of  stock  farming,  the  manure  produced  contains 
fertility  in  proportion  to  the  food  consumed.     If  good 
care  is  taken  of  the  manure,  and  in  place  of  the  grains 
sold,  mill  products  are  purchased  and  fed,  there  is  no 
loss  and  often  a  gain  of  fertility.     Between  these  two 
extremes,  exclusive  grain  farming  and  stock  farming, 
many  different  systems  of  farming  are  practiced  which 
remove  from  the  soil  various  amounts  of  fertility. 

(16) 


242  SOILS   AND   FERTILIZERS  . 

329.  Two  Systems  of  Farming  Compared.  —  The 

losses  of  fertility  from  farms  are  determined  by  the 
crops  and  products  sold,  the  care  of  the  manure,  and 
the  fertility  in  the  products  purchased  and  used  on  the 
farm.  If  an  account  were  kept  of  the  income  and 
outgo  of  the  fertility  of  farms,  it  would  be  found  that 
with  some  systems  the  soil  is  gaining  in  fertility,  while 
with  others  a  rapid  decline  is  occuring.  In  studying 
the  income  and  outgo  of  fertility,  it  is  necessary  to 
calculate  the  amounts  of  the  three  principal  elements, 
nitrogen,  phosphoric  acid,  and  potash  in  the  crops  and 
products  sold.  For  making  these  calculations  tables 
are  given  in  Sections  172  and  293.  In  the  handling 
of  manure  it  is  impossible  to  prevent  losses,  but  it  is 
possible  to  reduce  them  to  very  small  amounts. 
Hence  in  the  calculations,  a  loss  of  3  per  cent,  is  al- 
lowed for  mechanical  waste,  and  for  uneven  distribu- 
tion of  the  manure ;  that  is,  in  addition  to  the  fertility 
sold  from  the  farm  a  mechanical  loss  of  3  per  cent,  is 
allowed  for  all  crops  raised  and  consumed  as  food  by 
stock. 

On  one  farm  the  crops  raised  and  sold  are :  Flax  40 
acres,  wheat  50  acres,  oats  20  acres,  barley  50  acres ; 
no  stock  is  kept,  the  straw  is  burned,  and  the  ashes 
are  wasted. 

In  addition  to  the  nitrogen  removed  in  the  crops 
other  losses  must  be  considered.  Experiments  have 
shown  that  when  exclusive  grain  farming  is  practiced, 
for  every  pound  of  nitrogen  removed  in  the  crop,  four 
pounds  are  lost  from  the  soil  in  other  ways.  See 


CONSERVATION   OF   FERTILITY  243 

section  133.  This  would  make  the  total  loss  of  nit- 
rogen over  28,500  pounds  or  177  pounds  per  acre, 
which  large  as  it  may  seem  is  the  actual  loss  from 
the  soil  when  grain  only  is  raised  and  is  sold.  Ex- 
periments at  the  Minnesota  Experiment  Station 
showed  that  after  a  soil  had  been  cultivated  40  years, 
the  annual  loss  per  acre  of  nitrogen  in  exclusive 
wheat  raising  was  25  pounds  through  the  crop  and 
146  pounds  due  to  the  oxidation  of  the  nitrogenous 
humus  of  the  soil.18 

EXCLUSIVE  GRAIN  FARMING. 
Sold  from  the  Farm. 

Phosphoric 

Nitrogen.  acid.  Potash. 

^  Pounds.  Pounds.  Pounds. 

Flax,  40  acres 1600  600  800 

Flax  straw 600  120  320 

Wheat,  50  acres 1250  625  350 

Wheat  straw 500  375  1400 

Oats,  20  acres 700  240  200 

Oat  straw 300  1 20  700 

Barley,  50  acres 1400  750  400 

Barley  straw 600  250  1500 

Total 6950  3080  5670 

When  exclusive  grain  farming  is  followed,  the 
annual  losses  of  fertility  from  a  farm  of  160  acres  are 
28,500  pounds  of  nitrogen,  3000  pounds  of  phosphoric 
acid,  and  5500  pounds  of  potash. 

On  a  similar  farm  of  160  acres  the  crops  are  rotated 
as  described  in  Section  326.  The  amounts  of  fertility 
in  the  products  sold,  the  crops  raised  and  consumed 
as  fodder,  and  the  food  and  fuel  purchased,  are  given 
in  the  following  table. 


244  SOILS   AND   FERTILIZERS 

STOCK  FARMING. 
Sold  from  the  Farm. 

Phosphoric 

Nitrogen.          acid.  Potash. 

Pounds.          Pounds.  Pounds. 

Butter,  5000  pounds - ••         555 

Young  cattle,  10  head 200            190  16 

Hogs,  20 of  250  pounds  each. .     100              40  10 

Steers,  2 48              38  4 

Wheat,  10  acres 250            125  70 

Flax,  10  acres 390             150  190 

Rye,  10  acres 285             128  85 

Total 1278            676  380 

Raised  and  Consumed  on  the  Farm. 

Clover,  20  tons oo            270  600 

Timothy,  20  tons 600             180  800 

Corn,  20  acres 1500             300  800 

Corn  fodder,  i  acre 75              15  60 

Mangels,  2  acres 150               70  300 

Potatoes,  i  acre 40              20  75 

Straw,  40  tons 400            200  1000 

Peas,  5  acres 85  200 

Oats,  20  acres 700            240  200 

Barley,  20  acres  with  straw  •  •     800            400  760 

4265           1780  4795 
Mechanical  loss  of  food  con- 
sumed, 3  per  cent 128              53  144 

Food  and  Fuel  Purchased. 

Phosphoric 

Nitrogen.          acid.  Potash 

Pounds.        Pounds.  Pounds. 

Bran,  5  tons 275            260  150 

Shorts,  5  tons 250            150  100 

Oil  meal,  ton 100              35  25 

Hard-wood  ashes 25  100 

625            470  375 


CONSERVATION   OF   FERTILITY  245 

Mechanical   loss  in   material 

purchased  $%  T9  J4  Io 

Sold  from  farm 1278  676  380 

Loss  in  food  consumed,  etc..     128  53  144 


Total 1425  743  534 

Food  and  fuel  purchased 625  470  375 

Balance  lost  from  farm 800  273  159 

The  manure  produced  and  used  on  this  farm  results 
in  the  production  of  larger  crop  yields  than  is  the 
case  with  exclusive  grain  culture.  The  nitrogen 
gained  by  the  clover  and  peas  more  than  balances  the 
loss  of  nitrogen  in  other  crops.  Experiments  have 
shown  that  a  rotation  similar  to  this  caused  an  in- 
crease in  soil  nitrogen.18  Manure,  meadow  and  past- 
ure all  tend  to  increase  the  soil's  humus  and  nitrogen. 
The  losses  of  phosphoric  acid  and  potash  are  exceed- 
ingly small,  averaging  about  a  pound  per  acre  for 
each.  The  action  of  the  manure  on  this  farm  is  con- 
tinually bringing  into  activity  the  inert  plant  food 
of  the  soil  so  that  every  year  there  is  a  larger  amount 
of  more  active  plant  food,  which  results  in  producing 
larger  yields  per  acre. 

The  method  of  farming  has  a  marked  effect  upon 
crop  yields.  The  average  yield  of  wheat  in  those 
counties  in  Minnesota  where  live  stock  is  kept  and 
crops  are  rotated,  is  over  10  bushels  per  acre  greater 
than  in  similar  counties  where  exclusive  grain  farm- 
ing is  followed. 


246  SOILS   AND   FERTILIZERS 

Problems. 

Calculate  the  income  and  outgo  of  fertility  from  the  following 
farms. 

T.  Sold  from  the  farm  :  Wheat  40  acres,  oats  40  acres,  barley  40 
acres,  rye  20  acres,  flax  10  acres.  The  straw  is  burned  and  no  use 
is  made  of  any  manures. 

2.  Sold  from  the  farm  :  Wheat  20  acres,  barley  20  acres,  flax  5 
acres,  1000  pounds  of  butter,  10  hogs,  and  10  steers.     Purchased  : 
Bran  3  tons,  shorts  2  tons,  oil  meal  i  ton.     Crops  produced  and  fed 
on  farm  :     Clover  and  timothy  hay  40  tons,  corn  fodder  3  acres, 
corn  10  acres,  oats  and  peas  10  acres,  roots  i  acre,  millet  I  acre, 
and  barley  5  acres. 

3.  Sold  from  the  farm  :     Wheat  10  acres,  sugar  beets  5  acres, 
milk  100,000  pounds,  butter  500  pounds,  20  pigs,   6  head  of  young 
tock,  2  acres  of  potatoes.     Purchased  :  5  tons  of  bran,  2  tons  of 
oil  meal,  i  ton  of  cottonseed  meal,  15  cords  of  wood,  i  ton  of  acid 
phosphate,  1000  pounds  of  potassium  sulphate,  and  500  pounds  of 
sodium  nitrate.     Raised  and  consumed  on  the  farm  :  Corn  fodder 
15  acres,  mangels  i  acre,  peas  and  oats  5  acres,  clover  20  tons, 
timothy   10  tons,  straw  from  grain  sold,  oats    10  acres,    corn    20 
acres. 

4.  Calculate  the  income  and  outgo  of  fertility  from  your  own 
farm. 


CHAPTER  XIII 


PREPARATION   OF  SOILS  FOR  CROPS 

330.  Importance  of  Good  Physical  Condition  of 
Seed  Bed.  —  But  few  soils  are  in  suitable  condition 
for  seeding  without  farther  preparation  than  simply 
plowing  the  land.     If  the  plowing  is  poorly  done,  a 
good  seed  bed   cannot  be  prepared.     The  depth   of 
plowing  is  of  prime  importance  and  is  determined 
largely  by  the  character  of  the  soil,  as  sand,  clay  or 
loam.     (See  Section  35).     The  character  of  the  seed 
bed  is  influenced  not  only  by  the  depth  of  plowing  but 
by  the  nature  of  the  plowing  as  the  way  in  which  the 
furrow  slice  is  left.     Treatment  of  the  soil  after  plow- 
ing, as  disking,  harrowing,  cultivating  and  light  roll- 
ing must  be  determined  largely  from  the  character  of 
the  soil.     Too  frequently  the  preparation  of  the  soil 
is  not  given  sufficient  attention  and  crops  suffer  be- 
cause of  poorly  prepared  seed  beds. 

331.  Influence  of  Methods  of  Plowing  Upon  the 
Condition  of  the  Seed  Bed.  —  A  poor  seed  bed  is  some- 
times formed  by  complete  inversion  of  the  furrow  slice 
and  the  soil   not  being  sufficiently  pulverized.     If  a 
heavy  sod  has  simply  been  inverted,  subsequent  harrow- 
ing and  cultivation  will  fail  to  pulverize  and  loosen 
the  tough  sod  in  the  lower  part  of  the  furrow  slice. 


248  SOILS   AND   FERTILIZERS 

A  good  seed  bed  cannot  be  made  upon  such  a  foun- 
dation. When  the  land  is  plowed  so  that  the  furrow 
slice  is  left  at  an  angle  of  30  to  45  degrees,  the  surface 
is  corrugated  and  all  vegetation  is  buried  in  loose  soil. 
When  land  which  has  been  plowed  in  this  way  is  culti- 
vated and  harrowed,  a  better  seed  bed  is  formed  than 
is  possible  on  a  completely  inverted  furrow  slice. 


Fig.  35.     A  poor  way  of  plowing  sod  land  (after  Roberts). 


Fig.  36.     Plowed  land  left  in  good  condition  for  formation  of  seed 
bed  (after  Roberts). 

In  plowing,  it  should  be  the  aim  to  thoroughly  pul- 
verize the  soil,  completely  bury  all  surface  vegetation, 
and  leave  the  land  in  a  corrugated  condition  with  the 
furrow  slice  at  an  angle  but  firmly  connected  with  the 
subsoil.  The  plowing  should  cause  as  thorough  dis- 
integration of  the  soil  as  possible  and  this  can  best  be 
accomplished  by  the  use  of  a  plow  with  a  bold  rather 
than  too  flat  a  moldboard.  Roberts16  states  that  only 
about  10  per  cent,  of  the  energy  required  for  plowing 
is  used  by  the  friction  of  the  moldboard:  "  About  35 
per  cent,  of  the  power  necessary  to  plow  is  used  by  the 
friction  due  to  the  weight  of  the  plow,  and  55  per 
cent,  by  severing  the  furrow  slice  and  the  friction  of 


PREPARATION   OF   SOILS    FOR    CROPS  249 

the  land  slide."  In  the  preparation  of  the  seed 
bed,  it  is  economy  to  secure  as  much  pulverization  of 
the  soil  by  the  action  of  the  plow  as  possible  rather 
than  to  leave  too  much  for  subsequent  treatment. 

332.  Influence  of  Moisture  Content  of  the  Soil  at 
the  Time  of  Plowing.  —  The  condition  of  the  soil, 
particularly  as  to  moisture  content  at  the  time  of  plow- 
ing, has  much  to  do  with  the  production  of  a  good  seed 
bed.     If  soils  are  too  dry  when  plowed  they  fail  to 
pulverize,  and  disking,  harrowing,  and  in  some  cases 
light  rolling,  making  additional  expense,  must  be  re- 
sorted to  in  order  to  produce  a  fine,  mediumly  compact 
and  well  pulverized  seed  bed.     If  clay  soils  are  plowed 
when  too  wet,  the  pores  of  the  subsoil  become  clogged, 
a  condition  known  as  puddling  takes  place,  and  the 
furrow  slice  dries  and  forms  hard  lumps  and  clods. 
The  condition  in  which  the  soil  is  left  after  plowing, 
particularly  in  the  case  of  clay  soils,  has  much  to  do 
with  the  character  of  the  seed  bed  and  the  subsequent 
yield  of  crops. 

333.  Influence  Upon  the  Seed  Bed  of  Pulverizing 
and  Fining  the  Soil.  —  If  a  soil  is  lumpy,  and  the 
lower  strata  of  the  seed  bed   is   not  pulverized  and 
firmed,  the    soil   readily    loses  water   by   percolation, 
evaporation   takes   place    rapidly    and    the    crops  are 
poorly  fed  because  the  roots  are  unable  to  penetrate 
the  hard  lumps  and  secure  plant  food.     If  a  soil  is  in- 
clined to  be  lumpy,  the  cultivation  including  the  plow- 
ing should  be  carried  on  largely  with  the  view  of 
thoroughly  pulverizing  the  soil.     When  a  seed  bed  is 


250  SOILS   AND   FERTILIZERS 

well  prepared,  the  soil  warms  up  more  readily.  The 
loosening  and  pulverizing  of  the  land  enables  the  heat 
from  the  sun's  rays  to  more  readily  penetrate  the  soil 
and  bring  the  land  into  good  condition  for  promoting 
growth. 

334.  Aeration  of  Seed  Bed  Necessary.  —  Air  is 
required  for  functional  purposes  by  the  roots  of  crops. 
In  sand  and  loam  the  air  spaces  make  up  a  half  or  more 
of  the  total  volume.     With  such  soils  it  is  not  neces- 
sary to  cultivate  with  the  view  of  increasing  the  air 
spaces,  but  in  compact  soils,  as  heavy  clays,  plowing 
should  result  in  aeration  of  the  soil  and  an  increase  in 
the  number  of  air  spaces,  as  the  air  of  the  soil  takes  an 
important  part  in  rendering  plant  food  available.     (See 
Section  53).     If  soils  are  plowed  when  too  wet  they 
are  not  sufficiently  aerated.     The  amount  and  kind  of 
cultivation  to  secure  the  ventilation  and  aeration  neces- 
sary for  crop  production  must  be  regulated  according 
to  the  character  of  the  soil  as  sand,  clay  or  loam,  and  the 
climatic  conditions.     The  cultivation  which  is  given 
soils  for  purposes  of  conservation  of  the  moisture  also 
secures  the  proper  aeration. 

335.  Preparation  of  Seed  Bed  Without  Plowing. 
-  Loam  soils  which  have  been  subjected   to  a  sys- 
tematic rotation  of  crops  and  upon  which  corn  has  been 
grown,  need  not  be  plowed   but  the  seed  bed  for  the 
succeeding  grain  crop  can  be  prepared  simply  by  disk- 
ing.    Surface  tillage  of  the  corn  crop  has  sufficiently 
loosened  and  aerated  the  soil  and  has  caused  an  accu- 
mulation of  available  plant  food  near  the  surface  which 


PREPARATION   OF  SOILS   FOR   CROPS  251 

would  be  buried  and  be  less  available  to  the  crop  if 
the  land  were  plowed  too  deeply.  On  heavy  clay 
lands  this  method  of  preparing  the  seed  bed  without 
plowing  is  not  advisable  but  on  the  silt  soils  of  the 
northwest  it  is  a  practice  which  has  given  excellent 
results  and  is  beneficial  as  a  means  of  conserving  the 
soil  moisture. 

336.  Mixing  of  Sub-Soil  With  Seed  Bed.  —  Some 
soils  are  improved  by  deep  plowing  and  by  mixing 
the  surface  soil  and  sub-soil  to  form  the  seed  bed.     Such 
soils  are  usually  acid  in  character  and  contain  a  large 
amount  of  organic  matter,  in  which  case  the  mixing 
of  the  surface  soil  and  subsoil  improves  both  the  physi- 
cal and  chemical  properties  of  the  seed  bed.     In  the 
case  of  sandy  soils,  the  mixing  of  the  surface  soil  with 
the  sub-soil  is  not  advantageous  as  it  dilutes  the  stores 
of  plant  food  which  are  greater  in  the  surface  soil ; 
then  too  the  physical  properties  of  the  soil  are  not  im- 
proved.    The  combining  of  the  surface  soil  and  sub- 
soil in  the  case  of  heavy  clay  should  be   done  gradu- 
ally and  at  each  period  in  the  rotation  after  an  appli- 
cation of  farm  manure.     In  the  cultivation  of  clay 
soils,  it  should  be  the  aim  to  secure  a  deep  layer  of 
thoroughly  pulverized,  aerated  and  fertilized  soil.     In 
the  preparation  of  the  seed  bed  the  character  and  con- 
dition of   the  subsoil  is  equally  as  important  as  of  the 
surface  soil. 

337.  Cultivation  to  Destroy  Weeds.  —  One  of  the 

chief  objects  of  cultivation  is  to  destroy  weeds.  Cul- 
tivation for  this  purpose  should  be  given  early  in  the 


252  SOILS   AND    FERTILIZERS 

year  before  the  weeds  become  firmly  established. 
Weeds  are  most  easily  destroyed  at  the  time  of  germ- 
ination and  before  the  leaves  appear  above  ground. 
The  plow  should  be  relied  upon  largely  for  the  de- 
struction of  deep  rooted  perennial  weeds,  while  the 
cultivator  is  effectual  for  the  destruction  of  annuals. 
When  weeds  are  plowed  under  or  destroyed  by  culti- 
.vation  they  add  vegetable  matter  and  humus  to  the 
soil  and  thus  are  made  to  improve  the  condition  of 
the  soil  instead  of  reducing  the  yield  of  crops  by 
appropriating  fertility  as  they  do  if  allowed  to  grow 
and  mature.  Cultivation  which  secures  aeration  of 
the  soil  and  conservation  of  the  soil  moisture  is  also 
effectual  for  the  destruction  of  weeds. 

338.  Influence  of  Cultivation  Upon  Bacterial 
Action.  —  The  cultivation  of  the  soil  has  a  marked 
influence  upon  bacterial  action.  Some  of  the  soil 
organisms  as  the  nitrifying  organisms,  (See  Section 
139)  require  oxygen  for  their  existence,  hence  culti- 
vation which  increases  the  supply  of  oxygen  in  the 
soil  increases  the  activity  of  such  organisms.  In  acid 
peaty  soils,  aeration  induces  bacterial  action  which  re- 
sults in  more  rapid  decay  and  a  lowering  of  the.  per 
cent,  of  total  organic  matter  including  the  deleterious 
organic  acids.  The  neutralizing  of  the  organic  acids 
of  soils  by  applications  of  lime  and  wood  ashes  hastens 
bacterial  action.  During  the  process  of  nitrifica- 
tion, the  bacterial  action  is  not  alone  confined  to  the 
nitrogenous  compounds  of  the  soil,  the  nitrifying 
organisms  require  phosphates  as  food  which  are  left 


PREPARATION    OF   SOILS    FOR    CROPS  253 

after  nitrification  in  a  more  available  condition  as 
plant  food91.  The  mineral  as  well  as  the  organic 
matter  of  the  soil  is  subject  to  the  action  of  micro- 
organisms, and  the  cultivation  which  the  soil  receives 
can  be  made  either  to  accelerate  or  to  retard  this 
action.  Many  of  the  chemical  changes  which  take 
place  in  the  soil  resulting  in  the  liberation  of  plant 
food  are  induced  by  micro-organisms,  hence  the  rela- 
tion between  cultivation  of  the  soil  and  bacterial 
action.  Each  type  of  soil  has  its  own  characteristic 
microscopic  flora. 

339.  Inoculation  of  Soils.  —  In  old  soils  where 
the  process  of  nitrification  is  feeble,  it  has  been  pro- 
posed to  inoculate  the  soils  with  more  active  forms  of 
bacteria  so  as  to  make  the  inert  humus  nitrogen  more 
available  as  plant  food.  In  order  to  secure  the  best 
results  from  inoculation,  suitable  food  must  be  sup- 
plied for  the  organisms  and  any  adverse  condition,  as 
excess  of  acids  or  alkalies,  must  be  corrected.  Most 
soils  contain  the  requisite  soil  organisms  but  frequently 
they  are  unable  to  do  their  work  because  of  unfavor- 
able soil  conditions,  as  the  presence  of  injurious  matter 
or  the  lack  of  cultivation  or  food.  For  the  production 
of  legumes,  inoculation  of  the  soil  is  often  beneficial. 
The  commercial  production  and  distribution  of  the 
organisms  forming  the  nodules  on  the  roots  of  clover 
and  other  leguminous  crops  and  which  cause  fixation 
of  atmospheric  nitrogen,  was  first  proposed  and  inau- 
gurated by  Nobbe94 ;  later  a  modified  form  of  soil  in- 
oculation was  proposed  by  Moore87.  The  method 


254  SOILS   AND   FERTILIZERS 

of  inoculation  consists  in  first  multiplying  the  organ- 
isms in  water  containing  nutritive  substances,  and 
then  sprinkling  the  seeds  with  this  solution  diluted. 
Inoculation  with  soil  from  a  field  where  clover  or 
lupines  have  previously  been  grown  has  also  been  suc- 
cessful, particularly  in  reclaiming  sandy  waste  lands 
where  mineral  fertilizers  containing  potash  and  phos- 
phates are  used  to  furnish  these  elements  of  plant  food, 
while  the  more  expensive  nitrogen  is  acquired  indi- 
rectly from  the  air  through  the  clover.  Soils  in  a 
high  state  of  productiveness  are  not  usually  in  need 
of  inoculation  as  they  already  contain  all  of  the  essen- 
tial soil  organisms. 

340.  Cultivation  for  Special  Crops.  —  While  the 
general  principles  of  cultivation  apply  to  all  crops,  the 
extent  to  which  loosening  or  compacting  of  a  soil 
should  be  carried,  must  be  determined  by  the  charac- 
ter of  the  soil  and  the  crop  that  is  to  be  produced. 
The  methods  of  cultivation  must  be  varied  to  meet 
the  requirements  of  different  soils  and  different  crops. 
The  physical  requirements  of  the  soil  for  general  farm 
crops  are  discussed  in  Chapters  I.  and  XL  For  the 
production  of  a  special  crop,  the  cultivation  must  be 
adapted  to  the  specific  requirements  of  that  crop.  A 
knowledge  of  the  requirements  can  best  be  obtained 
by  a  study  of  the  subject  as  based  upon  experimental 
evidence.  The  cultivation  of  an  untried  crop  should 
not  be  attempted  on  a  large  scale  without  a  knowledge 
of  the  food  requirements  and  the  most  suitable  soil 
conditions.  The  production  of  sugar  beets  for 


PREPARATION   OF  SOILS   FOR   CROPS  255 

the  manufacture  of  sugar,  flax  for  fine  fiber,  or 
tobacco  under  shade,  requires  a  high  degree  of 
both  knowledge  and  skill.  For  the  production  of 
special  crops  the  preparation  of  the  seed  bed  and  the 
subsequent  cultivation  of  the  crop  are  matters  of  prime 
importance,  and  should  receive  careful  consideration 
on  the  part  of  the  cultivator.  Many  times  agricultural 
industries  undertaken  in  new  countries  have  failed 
because  the  cultivation  of  the  special  crop  used  in  the 
industry  has  not  been  successfully  accomplished  on 
account  of  lack  of  knowledge  of  the  cultural  methods 
necessary  for  successful  crop  production. 

341.  Cultivation  to  Prevent  Washing  and  Gully- 
ing of  Land.  —  In  regions  of  heavy  rain  fall,  rolling 
lands  of  clay  texture  often  become  gullied  by  the 
water  flowing  in  large  amounts  over  the  surface. 
Under  such  conditions  the  preparation  of  a  seed  bed, 
and  cultivation  of  the  soil  so  as  to  prevent  washing 
are  often  difficult  problems.  To  prevent  gullying,  the 
water  currents  should  be  divided  as  much  as  possible 
by  plowing  narrower  'lands'  and  by  increasing  the  num- 
ber of  shallow  dead  furrows.  The  larger  drains  should 
be  constructed  with  the  view  of  preventing  the  forma- 
tion of  deep  gullies,  this  can  in  part  be  accomplished 
by  encouraging  the  growth  of  special  grasses  with 
fibrous  roots  which  serve  as  soil  binders.  Soils  which 
gully  are  improved  by  the  addition  of  farm  manures 
and  other  humus  forming  materials  which  bind  the 
soil  particles ;  also  by  seeding  and  cultivating  at  right 
angles  to  the  slope  of  the  land  so  as  to  break  the  force 


256  SOILS   AND   FERTILIZERS 

of  the  water.  The  water  should  be  encouraged  to  per- 
colate through  the  soil  rather  than  to  flow  over  the 
surface.  (See  Section  25). 

342.  Bacterial  Diseases  of  Soils.  —  Many  of  the 
bacterial  diseases  to  which  crops  are  subject  are  caused 
primarily  by  a  diseased  condition  of  the  soil.  These 
diseases  can  often  be  held  in  check  by  the  right  kind 
of  cultivation,  by  securing  good  drainage  and  by  proper 
soil  ventilation  supplemented  with  the  application  of 
alkaline  matter  as  wood  ashes  and  land  plaster.  Both 
bacterial  and  fungus  diseases  of  soils  are  capable  of 
being  controlled  by  cultivation  particularly  when  the 
cultivation  improves  the  general  sanitary  condition  of 
the  soil.  With  the  improvement  of  the  sanitary  con- 
dition, there  is  less  liability  of  bacterial  diseases  becom- 
ing established  and  causing  destruction  of  the  crop. 
The  use  of  soil  disinfectants  is  possible  only  when  a 
small  area  is  involved  ;  they  are  not  applicable  to 
large  tracts  as  they  destroy  the  beneficial  as  well  as 
the  injurious  soil  organisms.  A  good  sanitary  condi- 
tion of  the  soil  is  as  essential  for  the  production  of 
crops  as  are  suitable  hygienic  surroundings  for  the 
rearing  of  live  stock.  Sunlight  and  air  are  important 
factors  in  bringing  about  an  improved  sanitary  condi- 
tion of  diseased  soils.  By  the  rotation  of  crops  many 
bacterial  diseases  as  flax  wilt  and  clover  sickness  are 
held  in  check.  Some  bacterial  diseases  are  dissemin- 
ated by  the  use  of  infected  seed.  By  sprinkling  the 
seed  grain  with  a  disinfectant  as  a  dilute  solution  of 
formalin  (i  pound  of  formalin  in  50  gallons  of  water) 


PREPARATION    OF   SOILS    FOR    CROPS  257 

bacterial  diseases,  as  grain  smuts  are  held  in  check. 
Low  forms  of  plants,  as  fungi,  also  develop  in  soils 
when  conditions  are  favorable,  and  they  take  an  im- 
portant part  in  changing  the  character  of  the  soil ; 
their  action  may  be  either  beneficial  or  injurious  de- 
pending upon  the  condition  of  the  soil.  Some  of  the 
organisms  which  are  propagated  in  the  soil  cause  bac- 
terial diseases  of  dairy  and  other  farm  products.  There 
is  a  very  close  relationship  between  soil  sanitation, 
crop  diseases,  and  the  quality  of  agricultural  products. 

343.  Influence  of  Crowding  Plants  in  the  Seed 
Bed.  —  The  number  of  plants  which  a  seed  bed  should 
produce  is  dependent  mainly  upon  the  supply  of  water 
and  plant  food.  By  means  of  thick  or  thin  seeding 
the  general  character  of  crops  may  be  influenced 
within  definite  limits.  Either  an  excessive  or  a  scant 
amount  of  seed  gives  poor  results.  If  over  crowded 
plants  fail  to  develop  normally  it  is  either  for  want  of 
plant  food  or  water  or  because  of  lack  of  room  for  de- 
velopment. Experiments  have  shown  that  excessive 
amounts  of  seed  wheat,  as  more  than  100  pounds  per 
acre  of  spring  wheat,  do  not  give  good  results.  Each 
crop  has  its  limits  beyond  which  it  is  not  desirable  to 
crowd  the  plants  in  the  seed  bed.  When  there  is  ex- 
cessive crowding,  unhygienic  conditions  prevail  and 
the  lack  of  air,  sunlight  and  good  ventilation  encourage 
bacterial  diseases,  while  on  the  other  hand  too  few 
plants  in  the  seed  bed  favor  the  growth  of  weeds  and 
an  abnormal  development  of  the  crop.  In  the  seeding 
of  grains  and  other  farm  crops,  the  amount  of  seed  to 


258  SOILS   AND    FERTILIZERS 

be  used  per  acre  should  be  determined  by  the  quality 
of  the  seed  and  the  local  conditions,  as  climate  and 
soil,  together  with  any  special  objects  desired  as  in- 
fluencing the  composition  and  character  of  the  crop. 

344.  Selection  of  Crops.  —  The  selection  of  the 
most  suitable  crops  to  be  grown  is  largely  a  local 
problem  and  must  be  determined  by  climatic  and  soil 
conditions.     The  preferences  of  farm  crops  for  certain 
types  of  soil  are  discussed  in  Sections  n  to  17,  and  it 
is  not  advisable  to  attempt  to  grow  crops  upon  soils 
to  which  they  are  not  naturally  adapted  or  under  un- 
favorable climatic   conditions.     Practical   experience 
is  the  best  guide  to  follow  in  regard   to  the  selection 
of  crops  or  the  most  suitable  line  of  farming  to  follow, 
and  it  will  be  found  that  this  experience  is  usually  in 
harmony  with  the  laws  governing  the  conservation 
of   the   fertility   of    the   soil.       Temporary   methods 
of  farming,  as  exclusive  grain  raising,  can  be  followed 
for  a  short  time  on  new  soils  but  it  is  desirable  that 
each   type  of  soil  should  be  subjected  to  a  judicious 
system  of  cultivation,  fertilizing  and  cropping  rather 
than  to  the  production  of  one  or  only  a  few  market 
crops  at  random.     The  selection   of  the  farm  crops 
and  their  utilization  for  market  or  feeding  purposes 
should  be  determined  mainly  by  the  system  of  farming 
that  is  best  adapted  to  the  soil  of  the  farm,  and  the 
farm   should  be  managed  largely  with  the  view  of 
maintaining  the  fertility  of  the  soil. 

345.  The  Inherent  and  Cumulative  Fertility  of 
Soils95.  —  There  is  present  in  nearly  every  soil  a  vari- 


PREPARATION   OF   SOILS   FOR   CROPS  259 

able  amount  of  inherent  fertility  produced  by  disin- 
tegration and  other  changes  to  which  soils  are  subject. 
In  some  long-cultivated  soils  the  amount  of  fertility 
produced  annually  by  weathering  and  natural  agencies 
is  sufficient  to  yield  from  10  to  15  bushels  of  wheat. 
This  does  not  represent  the  maximum  crop  producing 
power  of  the  soil  but  simply  the  inherent  or  natural 
fertility.  When  the  natural  fertility  is  reinforced 
with  farm  manures  and  other  fertilizers,  cumulative 
fertility  has  been  added  and  maximum  yields  of  crops 
are  secured.  In  many  soils  there  are  large  amounts 
of  cumulative  fertility  or  residues  from  former  appli- 
cations of  manures.  The  condition  of  a  soil  as  to  crop 
producing  power  is  dependent  both  upon  the  inherent 
and  the  cumulative  fertility,  as  well  as  upon  the 
mechanical  condition  of  the  soil.  In  the  production 
of  crops,  it  should  be  the  aim  to  utilize  all  of  the  in- 
herent fertility  to  the  best  advantage,  and  to  add  to 
the  cumulative  fertility  so  that  the  stock  of  total  fer- 
tility may  be  increased.  Soils  of  the  highest  fertility 
are  those  which  are  composed  of  a  large  amount  of 
silt  or  particles  of  equivalent  value,  are  well  drained,  but 
sufficiently  retentive  of  moisture  for  crop  production, 
and  are  of  good  capillarity.  Such  soils  have  usually 
been  deposited  by  water ;  they  are  uniform  in  texture, 
of  great  depth  and  contain  large  amounts  of  organic 
matter  rich  in  nitrogen  and  mineral  matter  contain- 
ing all  of  the  essential  elements  of  plant  food.  When 
such  soils  are  cultivated,  the  organic  matter  readily 
undergoes  decay  with  liberation  of  plant  food. 

346.     Balanced  Soil  Conditions.  —  A  high  state  of 


260  SOILS   AND    FERTILIZERS 

fertility  necessitates  a  balanced  condition  of  the  physi- 
cal and  chemical  properties  of  a  soil.  Some  soils  are 
of  good  texture  and  have  all  of  the  necessary  physical 
requisites  for  crop  production  but  fail  to  produce  good 
crops  because  of  a  scant  supply  of  the  essential  ele- 
ments of  plant  food.  Other  soils  contain  the  neces- 
sary plant  food  but  are  unproductive  because  of  poor 
physical  conditions.  Soils  may  be  unproductive  on 
account  of  either  chemical  or  physical  defects  causing 
an  unbalanced  condition  of  the  various  factors  of  soil 
fertility.  In  the  cultivation  of  a  soil  it  should  be  the 
aim  to  discover  any  defect  and  then  to  apply  the 
necessary  corrective  measures.  Soil  problems  are  ex- 
tremely varied  in  character  and  the  cultivator  of  the 
soil  should  seek  aid  jointly  from  the  sciences  of  chem- 
istry, physics,  biology  and  geology,  and  also  from  prac 
tical  experience  founded  upon  observations  in  the 
cultivation  of  soils  and  the  production  of  crops.  The 
utilization  and  maintenance  of  the  fertility  of  the  soil 
necessarily  form  the  basis  of  any  rational  agricultural 
system. 


CHAPTER  XIV 


LABORATORY  PRACTICE 

The  laboratory  practice  is  an  essential  part  of  the  work  in  Soils 
and  Fertilizers  as  the  experiments  illustrate  many  of  the  funda- 
mental principles  of  the  subject.  The  student  should  endeavor  to 
cultivate  his  powers  of  observation  so  as  to  grasp  the  principles  in- 
volved in  the  work  rather  than  to  do  it  in  a  mere  mechanical  or 
perfunctory  way.  Neatness  is  one  of  the  essentials  for  success  in 
laboratory  practice  ;  an  experiment  performed  in  a  slovenly  way  is 
of  but  little  value. 

A  careful  and  systematic  record  of  the  laboratory  work  should  be 
kept  by  the  student  in  a  suitable  note-book.  In  recording  the  re- 
sults of  an  experiment  the  student  should  give  in  a  clear  and  con- 
cise form  the  following  : 

1 i )  Title  of  the  experiment. 

(2)  How  the  experiment  is  performed. 

(3)  What  was  observed. 

(4)  What  the  experiment  proves. 

The  note-book  should  be  a  complete  record  of  the  student's  in- 
dividual work,  and  should  be  written  up  at  the  time  the  experi- 
ments are  performed. 

The  student  is  advised  to  review  at  the  time  the  experiments  are 
performed  those  topics  presented  in  the  text  which  have  a  bearing 
upon  the  experiments,  so  that  a  clearer  conception  can  be  gained 
of  the  relationship  between  the  laboratory  work  and  that  of  the 
class  room. 

Students  who  have  had  but  little  laboratory  practice  are  advised 
to  study  the  chapters  on  Laboratory  Manipulation,  and  Water  and 
Dry  Matter,  given  in  "  The  Chemistry  of  Plant  and  Animal  Life." 

Some  of  the  pieces  of  apparatus  are  loaned  to  the  student  when 
needed  to  perform  the  experiment ;  for  this  apparatus  a  receipt  is 
taken,  and  the  student  is  credited  with  the  apparatus  when  it  is 
returned.  The  following  are  supplied  to  each  student : 


262 


SOILS   AND    FERTILIZERS 


Crucible  Tongs. 

Pkg.  Filter  Paper. 

Test  Tube  Clamp. 

Evaporator. 

Stirring  Rod. 
3  Beakers. 
6  Test  Tubes, 
i  Test  Tube  Stand, 
i  Funnel, 
i  Mortar  and  Pestle. 


2  Bottles. 
Large  Cylinder. 
Sand  Bath. 
Hessian  Crucible. 
Wooden  Stand. 
Tripod. 

Ring  Stand  and  3  Rings. 
Single  Clamp. 

Burner  and  2Ft.  RubberTubing 
Brush. 


The  student  should  plan  to  make  judicious  use  of  his  time  while 
in  the  laboratory. 

Experiment  No.  i. 

Determination  of  the  Hydroscopic  Moisture  of  Soils. 
Weigh  in  grams  to  the  second  decimal  place  an  aluminum  dish 


Fig.  37.    Apparatus  for  Determining  Moisture  Content  of  Soils. 
or  tray.     Place  about  ten  grams  of  air  dry  soil  in  the  dish  and 
weigh  again.     Then  place  the  dish  containing  the  soil  in  the  water 


EXPERIMENTS  263 

oven  and  leave  it  four  hours  for  the  soil  to  dry.  Cool  and  weigh 
at  once  so  there  may  be  as  little  absorption  of  water  from  the  air 
as  possible.  From  the  loss  of  weight,  calculate  the  per  cent,  of 
hydroscopic  moisture  in  the  soil.  (Soils  from  the  students'  home 
farms  are  to  be  used  in  experiments Nos.  i,  2,  4,  6,  9,  12,  14,  16,  17, 
and  19,  each  student  working  with  his  own  soil). 

Experiment  No.  2. 
Determination  of  the  Capacity  of  Loose  Soils  to  Absorb  Water. 

To  100  grams  of  air  dry  soil  in  a  beaker,  add  100  cc.  of  water. 
Mix  the  soil  and  water,  then  pour  the  mixture  on  a  filter  paper 
fitted  into  a  funnel  and  previously  saturated,  but  not  dripping. 
For  transferring  the  soil,  50  cc.  more  water  may  be  used.  Measure 
the  drain  water  in  a  graduate.  To  prevent  evaporation,  keep  the 
moist  soil  in  the  funnel  covered  with  a  glass  plate.  Deduct  the 
leachings  from  the  total  water  used.  Calculate  the  per  cent,  of 
waiter  retained  by  the  air  dry  soil. 

Repeat  the  experiment,  using  sand,  and  note  the  difference  in 
absorptive  power. 

Repeat,  using  95  per  cent,  of  sand  and  5  per  cent,  of  dry  and 
finely  pulverized  manure. 

Experiment  No.  3. 

Determination  of  the  Capillary  Water  of  Soils. 
For  this  experiment,  a  sample  of  soil  directly  from  the 
field  is  to  be  used.  The  sample  is  to  be  taken  at  a  depth 
of  from  3  to  9  inches  or  at  any  depth  desired.  One  hundred 
grams  of  soil  are  weighed  into  a  tarred  drying  pan,  exposed 
in  a  thin  layer  to  the  room  temperature  for  twenty-four  hours  and 
then  reweighed.  After  an  interval  of  from  two  to  four  hours  the 
soil  is  weighed  again,  and  if  the  weight  is  fairly  constant  the  per 
cent,  of  water  lost  by  air  drying,  representing  the  capillary  water 
of  the  soil  at  the  time  of  sampling,  is  calculated.  If  desired  this 
experiment  can  be  repeated,  using  different  types  of  soil,  as  sand, 
clay  and  loam. 

Experiment  No.  4. 
Capillary  Action  of  Water  Upon  Soils. 

Firmly  tie  a  piece  of  linen  cloth  over  the  end  of  along  glass  tube 
4  inches  in  diameter,  then  fasten  a  piece  of  wire  gauze  over  the 


264 


SOILS   AND    FERTILIZERS 


cloth.  Fill  the  tube  with  sandy  soil  (No.  i).  Compact  the  soil 
after  the  addition  of  each  measured  quantity  of  soil  by  allowing  the 
weight  from  the  compaction  machine  to  drop  twice  from  the  12 
inch  mark. 


Fig.  38.    Capillary  Action  of  Water  on  Soils. 

In  a  similar  way,  fill  a  second  and  a  third  tube  respectively  with 
clay  and  loam  ;  then  immerse  the  lower  ends  of  the  tubes  in  a 
cylinder  of  water  and  support  the  tubes,  as  shown  in  the  illustra- 
tion. Measure  each  day  for  one  week  the  height  to  which  the 
water  rises  in  the  soils.  If  desired,  three  additional  tubes  filled 
loosely  with  the  soils  can  be  used,  and  the  influence  of  compaction 
upon  the  capillary  rise  of  water  in  the  soils  noted. 

Experiment  No.  5. 
Influence  of  Manure  and  Shallow  Surface  Cultivation  Upon  the 

Moisture  Content  and  Temperature  of  Soils. 
Weigh  and  fill  four  boxes,  each  a  foot  square  and  a  foot  deep,  as 


EXPERIMENTS 


265 


follows  :  One  with  air  dry  sand,  one  with  clay,  one  with  loam,  and 
one  with  sand  containing  5  per  cent,  of  fine  dry  manure.  Deter- 
mine the  hydroscopic  moisture  of  each  sample.  Weigh  the  boxes 
after  adding  the  soils  which  should  be  moderately  compacted.  To 
each  add  the  same  amount  of  water  slowly  from  a  sprinkling  pot, 
carefully  measuring  the  water  used.  The  soil  should  be  well 
moistened,  but  not  supersaturated.  Each  box  is  to  receive  shal- 
low surface  cultivation,  using  for  the  purpose  a  gardener's  small 
tool.  Leave  the  boxes  exposed  to  the  sun  or  in  a  moderately  warm 
room.  At  the  end  of  two  or  three  days  take  a  sample  of  soil  from 
the  center  of  each  box  at  a  depth  of  four  inches  and  determine  the 
moisture  content  as  directed  in  Experiment  No.  i.  Note  the  differ- 
ences in  moisture  content.  Weigh  the  boxes.  Take  the  tempera- 
ture of  the  soil  in  each  box. 

Experiment  No.  6. 
Weight  of  Soils. 

Determine  the  cubic  contents  of  a  box  about  4  inches  square. 
Weigh  the  box.  Determine  its  weight  when  filled,  not  compacted, 
wTith  air  dry  sand,  with  clay,  with  loam  and  with  peaty  soil.  Com- 
pute the  weight  per  cubic  foot  of  each  soil. 


Fig.  39.     Determining  the  Weight  of  Soils. 

Experiment  No.  7. 

Influence  of  Color  Upon  the  Temperature  of  Soils. 

Expose  to  the  sun's  rays,  dry  clay,  dry  sand,   and  moist  and  dry 

peat.     After  two  hours  exposure  take  the  temperature  of  each. 

The  bulb  of  the  thermometer  should  just  be  covered  with  the  soil. 

All  of  the  observations  should  be  made  under  uniform  conditions. 


266  SOILS   AND   FERTILIZERS 

Experiment  No.  8. 
Movement  of  Air  Through  Soils. 

Fill  a  tube  12  inches  high  and  3  inches  in  diameter  with  sifted 
loam  soil  without  compacting.  Attach  the  soil  tube  to  the  aspira- 
tor by  means  of  a  rubber  tube.  Note  the  time  required  to  draw  5 
liters  of  air  through  the  soil.  In  like  manner  fill  tubes  with  sand, 


Fig.  40.     Apparatus  to  Determine  Rate  of  Air  Movement  Through  Soils. 
(Adapted  from  Bui.  107,  U.  S.  Dept.  Agr.,  Office  of  Expt.  Stations). 

gravel,  peat,  and  clay,  and  determine  the  time  required  for  5  liters 
of  air  to  be  aspirated  through  each.  In  filling  the  tubes,  care 
should  be  taken  that  all  are  treated  alike.  Repeat  the  experiment 
using  soil  from  your  own  farm  loosely  filling  one  tube,  and  mod- 
erately compacting  another  tube  with  the  compacting  machine. 
Note  the  difference  in  the  time  required  for  the  air  to  pass  through 
the  loose  and  the  compact  soil. 

Experiment  No.  9. 
Separation  of  Sand,  Silt  and  Clay. 

For  this  experiment,  the  student  should  use  some  of  the  soil 
from  his  home  farm.  Ten  grams  of  soil  which  have  been  passsd 
through  a  sieve  with  holes  .5  mm.  in  diameter  are  placed  in  a  mor- 


EXPERIMENTS  267 

tar,  and  about  20  cc.  of  water  added.  The  soil  is  pestled  with  a 
rubber  tipped  pestle  with  the  object  of  separating  adhering  parti- 
cles without  pulverizing  the  individual  soil  grains.  After  two  or 
three  minutes  rubbing,  more  water  is  added  and  the  soil  and  water 
are  allowed  to  sediment  for  about  one  minute  ;  the  turbid  liquid  is 
then  decanted  into  a  beaker.  This  process  of  soft  pestling  and 
decantation  is  repeated  two  or  three  times  until  the  remaining  soil 
grains  appear  free  from  adhering  smaller  particles.  With  some 
soils  this  is  a  tedious  process.  The  contents  of  the  mortar  are  then 
transferred  to  the  beaker  and  enough  water  is  added  to  nearly  fill 
the  beaker.  The  contents  of  the  beaker  are  thoroughly  stirred, 
and  after  three  to  five  minutes  sedimentation,  the  turbid  liquid  is 
decanted  into  a  second  beaker  leaving  the  sediment  in  the  first 
beaker.  More  water  is  added  to  the  first  beaker  and  the  process 
of  stirring,  sedimentation  and  decantation  are  repeated  until  the 
sediment  consists  mainly  of  clean  and  fine  sand.  The  turbid  liquid 
in  the  second  beaker  is  decanted  into  a  large  cylinder  ;  the  sedi- 
ment in  the  second  being  washed  with  more  water  and  the  wash- 
ing added  to  the  cylinder.  It  is  to  be  noted  that  the  sediment  in 
the  second  beaker  is  composed  of  finer  particles  than  the  sediment 
in  the  first  beaker.  The  sediment  in  the  first  beaker  consists 
mainly  of  medium  and  fine  sand,  and  in  the  second  beaker,  of  fine 
sand  and  coarse  silt.  Some  sand  particles  are  carried  along  in  the 
washings  into  the  large  cylinder.  It  is  difficult  to  make  even  an 
approximate  separation  of  a  soil  into  sand,  silt  and  clay  particles. 
In  the  mechanical  analysis  of  soil,  the  chemist  uses  the  microscope 
to  determine  when  the  separations  are  reasonably  complete.  The 
sediment  in  the  cylinder  consists  mainly  of  silt.  The  fine  parti- 
cles which  remain  suspended  in  the  water  of  the  cylinder  and 
cause  the  roiled  appearance  are  mainly  the  clay  particles.  In  this 
experiment  note  approximately  what  grades  of  soil  particles  pre- 
dominate in  your  soil.  Save  the  liquid  in  the  cylinder  for  the  next 
experiment. 

Experiment  No.  10. 
Sedimentation  of  Clay. 

In  each  of  three  separate  cylinders  or  beakers  place  200  cc.  of  the 
turbid  liquid  saved  from  Experiment  No.  9.  To  beaker  No.  I,  add 
.5  gm.  calcium  hydroxid  and  stir.  To  beaker  No.  2,  add  i  gm. 
of  calcium  hydroxid  and  stir.  The  third  beaker  is  used  for  pur- 


268  SOILS   AND   FERTILIZERS 

poses  of  comparison  and  no  calcium  hydroxide  is  added.  After  24 
hours  examine  the  three  beakers  and  note  the  influence  of  the  cal- 
cium hydroxid  in  precipitating  the  clay  and  clarifying  the  liquid. 

Experiment  No.  n. 

Properties  of  Rocks  from  which  many  Soils  are  Derived. 
Study  the  laboratory  samples  of  rocks  and  fill  out  the  following 
table  : 

Comparative  General          vSoluble 

Rocks.  Hardness.  Color.  Form.  in  HC1 


Feldspar  .... 

Mica 

Quartz 

Granite 

Hornblende.  .   . 
limestone  .   .   . 


Experiment  No.  12. 
Form  and  Size  of  Soil  Particles. 

(Note.  Special  directions  for  manipulating  the  microscope, 
placing  the  material  on  the  microscopical  slide,  and  focusing  will 
be  given  by  the  instructor). 

Place  on  a  microscopical  object  slide  a  small  amount  of  soil,  dis- 
tribute it  in  a  thin  layer,  as  directed  by  the  instructor,  and  examine 
with  a  low  power  microscope.  Observe  the  form  and  size  of  the 
soil  particles,  distinguish  the  various  grades  of  sand,  silt  and 
clay,  and  make  drawings  of  some  of  the  particles. 

Experiment  No.  13. 
Pulverized  Rock  Particles. 

Examine  with  a  low  power  microscope  samples  of  pulverized 
mica,  feldspar,  granite,  and  limestone.  Note  any  similarity  to  the 
soil  particles  examined  in  Experiment  No.  12. 

Experiment  No.  14. 

Reaction  of  Soils. 

For  this  experiment  use  peaty,  mildly  alkaline  and  clay  soils. 
Bring  in  contact  with  each  soil,  moistened  with  distilled  water, 
pieces  of  sensitive  red  and  blue  litmus  paper.  Note  any  changes 
in  color  of  the  litmus  paper  and  state  what  the  results  show.  In 
a  similar  way  test  the  soil  from  your  own  farm . 


EXPERIMENTS  269 

Experiment  No.  15. 
Absorption  of  Gases  by  Soils. 

Weigh  50  grams  of  soil  into  a  wide  mouthed  bottle,  add  50  cc.  of 
wgter  and  i  cc.  of  strong  ammonia.  Note  the  odor.  Cork  the 
bottle,  shake,  and  after  24  hours  again  note  the  odor.  To  what  is 
the  absorption  of  the  ammonia  due?  Is  this  a  physical  or  a  chem- 
ical change.  Define  fixation. 

Experiment  No.  16. 
Acid  Insoluble  Matter  of  Soils. 

Weigh  10  grams  of  soil  into  a  beaker,  add  100  cc.  hydrochloric 
acid  (50  cc.  strong  acid  and  50  cc.  H2O);  cover  the  beaker  with  a 
watch  glass  ;  heat  on  the  sand  bath  in  the  hood  for  two  hours,  re- 
placing the  acid  solution,  if  necessary,  in  case  excessive  evapora- 
tion takes  place.  Filter,  transfer  and  wash  the  residue,  using  50 
cc.  distilled  water.  Note  the  appearance  and  quantity  of  insoluble 
residue.  Of  what  does  it  consist  ?  What  is  its  value  as  plant  food  ? 
How  does  it  resemble  the  original  soil  and  in  what  ways  does  it 
differ?  Save  the  filtrate  for  the  next  experiment. 

Experiment  No.  17. 
Acid  Soluble  Matter  of  Soils. 

Divide  the  filtrate  from  the  preceding  experiment  into  three 
equal  portions,  (i)  To  one  portion  add  ammonia  until  alkaline. 
The  precipitate  formed  consists  of  iron  and  aluminum  hydroxid  and 
phosphoric  acid.  Note  the  color  and  gelatinous  appearance  of  this 
precipitate.  When  dried  it  occupies  only  a  small  volume.  Filter 
and  remove  this  precipitate.  This  filtrate  contains  lime,  magnesia, 
potash  and  soda.  To  the  filtrate  add  20  cc.  of  ammonium  oxalate, 
warm  on  the  sand  bath  and  note  any  precipitate  of  calcium  oxalate 
that  is  formed.  (2)  Evaporate  the  second  portion  nearly  to  dry- 
ness.  Add  20  cc.  distilled  H2O  and  3  cc.  HNO3 ;  warm  to  dissolve 
any  residue.  Add  5  to  7  cc.  of  ammonium  molybdate,  heat  gently 
and  shake.  The  precipitate  is  ammonium  phosphomolybdate, 
which  contains  the  element  P  in  chemical  combination.  (3) 
Evaporate  third  portion  in  the  evaporating  dish  on  the  sand  bath. 
What  does  the  residue  consist  of  and  what  elements  does  it  con- 
tain? 


270  SOILS   AND    FERTILIZERS 

Experiment  No.  18. 
Extraction  of  Humus  from  Soils. 

Ten  grams  of  soil  are  placed  in  a  bottle  (preferably  a  glass  stop- 
pered one)  and  200  cc.  H2O  and  5  cc.  HC1  added.  Shake  aad 
allow  10  to  24  hours  for  the  acid  to  dissolve  the  lime  so  that  the 
humus  can  be  dissolved  by  the  alkali.  Filter  the  acid  and  wash 
the  soil  on  the  filter  with  distilled  water  until  the  washings  are  no 
longer  acid  to  litmus  paper.  Transfer  the  soil  to  the  bottle  again, 
add  loo  cc.  H2O  and  5  cc.  KOH  solution.  Shake,  and  after  two  to 
four  hours  filter  off  some  of  the  solution,  which  is  dark-colored 
and  contains  dissolved  humus  compounds. 

To  10  cc.  of  the  filtered  humus  solution,  add  HC1  until  neutral. 
The  precipitate  that  is  formed  is  mainly  humic  acid  and  soil 
humates.  Evaporate  a  second  portion  of  10  to  20  cc.  to  dryness  ; 
the  black  residue  obtained  is  humus  material  extracted  from  the 
soil. 

Experiment  No.  19. 
Nitrogen  in  Soils. 

Mix  5  grams  of  soil  and  an  equal  bulk  of  soda  lime  in  a  mortar  ; 
transfer  to  a  strong  test  tube.  Connect  the  test  tube  with  a  deliv- 
ery tube  which  leads  into  another  test  tube  containing  distilled 
water.  Heat  cautiously  the  test  tube  containing  the  soil  and  soda 
lime  with  the  Bunsen  burner,  for  from  5  to  10  minutes.  Test  the 
liquid  with  litmus  paper  and  note  the  reaction.  Soda  lime  aided 
by  heat  decomposes  the  organic  matter  of  the  soil  and  forms  CO2> 
H2O  and  NH3.  The  nitrogen  in  the  form  of  ammonia  is  distilled 
and  absorbed  by  the  water  in  the  second  test  tube  ;  the  reaction 
is  due  to  the  presence  of  the  ammonia. 

Experiment  No.  20. 

Testing  for  Nitrates. 

Dissolve  about  50  milligrams  of  sodium  or  potassium  nitrate  in 
loo  cc.  H2O.  To  15  cc.  of  this  solution,  add  2  cc.  of  a  dilute  and 
clear  solution  of  FeSO4,  and  place  the  test  tube  in  a  cylinder. 
Through  a  long  stemmed  funnel  add  2  or  3  cc.  H2SO4.  Observe 
the  dark  brown  ring  that  is  formed  ;  H2SO4  liberates  HNO3  as  a 
free  acid,  which  in  turn  changes  the  iron  from  the  ferrous  to  the 
ferric  state  ;  the  dark  brown  color  is  due  to  the  nitric  acid  forming 
intermediate  iron  compounds  during  this  operation. 


EXPERIMENTS  271 

Experiment  No.  21. 
Volatilization  of  Ammonium  Salts. 

In  separate  test  tubes,  place  about  .1  gtn.  each  of  ammonium  car- 
bonate and  ammonium  sulphate.  Apply  heat  gently  to  each  and 
observe  the  result.  Observe  that  the  ammonium  carbonate  readily 
volatilizes  and  some  is  deposited  on  the  walls  of  the  test  tube  while 
the  ammonium  sulphate  is  much  less  volatile.  In  poorly  venti- 
lated barns,  deposits  of  ammonium  carbonate  are  frequently  found. 

Experiment  No.  22. 
Testing  for  Phosphoric  Acid. 

Dissolve  .5  gm.  bone  ash  in  15  cc.  H2O  and  3  to  5  cc.  HNO3  and 
filter.  To  the  warm  filtrate,  add  5  to  7  cc.  ammonium  molybdate 
and  shake.  The  yellow  precipitate  formed  is  ammonium  phospho- 
molybdate.  See  Experiment  No.  17. 

Experiment  No.  23. 

In  a  test  tube,  heat  .5  gm.  of  bone  ash  with  20  cc.  distilled 
H2O  ;  filter.  To  the  warm  filtrate,  add  5  cc.  ammonium  molyb- 
date and  shake.  Note  the  result  as  compared  with  that  when 
HNO3  was  used  with  the  distilled  water.  What  does  the  result 
show  ? 

Experiment  No.  24. 
Preparation  of  Acid  Phosphate. 

Place  100  gms.  bone  ash  in  a  large  lead  dish.  Add  slowly  and 
with  constant  stirring  100  gms.  commercial  sulphuric  acid,  using 
an  iron  spatula  for  the  purpose.  Transfer  the  mixture  to  a  wooden 
box  and  allow  it  to  act  for  about  three  days.  Then  pulverize  and 
examine.  The  mixing  of  the  acid  and  phosphate  should  be  done 
in  a  place  where  there  is  a  good  draft.  Test  yz  gram  for  water 
soluble  phosphates  as  directed  in  Experiment  No.  23. 

Experiment  No.  25 

Solubility  of  Organic  Nitrogenous  Compounds  in  Pepsin  Solution. 
Prepare  a  pepsin  solution  by  dissolving  5  gms.  of  commercial 
pepsin  in  a  litre  of  water,  adding  i  cc.  of  strong  HC1.  Place  in 
separate  beakers  .5  gm.  each  of  dried  blood,  tankage  and  bone  ash. 
Add  200  cc.  of  pepsin  solution  to  each  and  place  the  beakers  in  a 
water  bath  kept  at  a  temperature  of  about  40  deg.  C.  Stir  occasion- 


272  SOILS   AND   FERTILIZERS 

ally,  and  at  the  end  of  five  hours  observe  the  comparative  amounts 
of  insoluble  matter  remaining  in  the  beakers,  also  the  color  and 
appearance  of  the  solution  in  each  beaker.  See  Section  158. 

Experiment  No.  26. 
Preparation  of  Fertilizers. 

Mix  in  a  box  200  gms.  acid  phosphate,  (saved  from  Experiment 
24)  50  grams  kainit,  and  50  gms.  sodium  nitrate.  Calculate  the 
percentage  composition  of  this  fertilizer  and  its  trade  value. 

Experiment  No.  27. 

Testing  Ashes. 

Test  samples  of  leached  and  unleached  ashes  in  the  way  de- 
scribed in  Section  240. 

Experiment  No.  28. 

Extracting  Water  Soluble  Materials  from  a  Commercial  Fertilizer. 
Dry  and  weigh  a  7  cm.  filter  paper.  Fit  it  in  a  funnel,  and  place 
in  it  2  gms.  of  commercial  fertilizer.  Pass  through  the  filter,  a 
little  at  a  time,  a  half  litre  of  pure  water  at  about  40  deg.  C.  (dis- 
tilled water  preferred).  Transfer  the  filter  paper  and  contents  to 
a  watch  glass,  dry  in  a  water  oven,  weigh  and  calculate  the  per 
cent,  of  material  extracted  by  the  water.  If  the  fertilizer  is  made 
of  such  materials  as  acid  phosphate,  kainit,  muriate  or  sulphate  of 
potash,  nitrate  of  soda  and  sulphate  of  ammonia,  from  60  to  90  per 
cent,  will  dissolve.  Inspect  the  insoluble  residue  and  note  if  it  is 
composed  of  dried  blood,  bones  or  animal  refuse  materials.  In  a 
high  grade  complete  commercial  fertilizer,  from  40  to  80  per  cent, 
or  more  should  dissolve  in  water. 

Experiment  No.  29. 

Influences  of  Continuous  Cultivation  and  Crop  Rotation  upon  the 
Properties  of  Soils. 

For  this  experiment,  a  soil  that  has  been  under  continuous  culti- 
vation, and  also  one  of  a  similar  character  from  an  adjoining  field 
where  the  crops  have  been  rotated  and  farm  manures  have  been 
applied,  should  be  used.  Make  the  following  determinations  with 
each  soil : 

Weight  per  cubic  foot. 

Capacity  to  hold  water. 


EXPERIMENTS  273 

Note  the  color  of  each,  and  the  percentages  of  nitrogen  and 
humus  obtained  by  chemical  analysis. 

Experiment  No.  30. 
Summary  of  Results  of  Tests  with  Home  Soil. 

Hydroscopic  moisture  as  determined  in  Experiment  No.  i. 

Capacity  of  the  loose  soil  to  absorb  water  in  Experiment  No.  2. 

Height  of  rise  of  capillary  water  in  tube  in  Experiment  No.  4. 

Weight  per  cubic  foot  in  Experiment  No.  6. 

Prevailing  kind  of  soil  particles  in  Experiment  No.  9. 

Reaction  of  soil  in  Experiment  No.  14. 

Amount  of  acid  soluble  matter  in  Experiment  No.  17. 

Amount  of  humus  extractive  material  in  Experiment  No.  18. 

Amount  of  lime. 

Crops  most  suitable  for  production  upon  this  soil  as  indicated  by 
physical  and  chemical  tests. 

How  does  this  agree  with  your  experience  with  the  crops  raised 
on  the  soil  ? 

Probable  deficiencies  or  weak  points  as  indicated  by  tests  or  past 
experience. 

What  is  the  most  suitable  line  of  farming  to  follow  with  this  soil 
in  order  to  conserve  its  fertility  ? 

Scheme  of  Soil  Classification. 

(Adapted  from  Bureau  of  Soils  Report,  U.  S.  Dept.  Agr). 

Coarse  sand  contains  more  than  20  per  cent,  of  coarse  sand  and 
more  than  50  per  cent,  of  fine  gravel,  coarse  sand,  and  medium 
sand,  less  than  10  per  cent,  of  very  fine  sand,  less  than  15  per  cent, 
of  silt,  less  than  10  per  cent  of  clay,  and  less  than  20  per  cent,  of 
silt  and  clay. 

Medium  sand  contains  less  than  10  per  cent,  of  fine  gravel,  more 
than  50  per  cent,  of  coarse,  medium,  and  fine  sand,  less  than  10 
per  cent,  of  very  fine  sand,  less  than  15  per  cent,  of  silt,  less  than 
10  per  cent,  of  clay,  and  less  than  20  per  cent,  of  silt  and  clay. 

Fine  sand  contains  less  than  10  per  cent,  of  fine  gravel  and 
coarse  sand,  more  than  50  per  cent,  of  fine  and  very  fine  sand,  less 
than  15  per  cent,  of  silt,  less  than  10  per  cent,  of  clay,  and  less 
than  20  per  cent,  of  silt  and  clay. 

Sandy  loam  contains  more  than  20  per  cent,  of  fine  gravel,  coarse 
sand  and  medium  sand,  more  thanr2o  per  cent,  and  less  than  35 

(18) 


274  SOILS   AND    FERTILIZERS 

per  cent,  of  silt,  less  than  15  per  cent,  of  clay,  and  less  than  50  per 
cent,  of  silt  and  clay. 

Fine  sandy  loam  contains  more  than  40  per  cent,  of  fine  and 
very  fine  sand  and  more  than  20  per  cent,  and  less  than  50  per 
cent,  of  silt  and  clay,  usually  containing  10  to  35  per  cent,  of  silt 
and  from  5  to  15  per  cent,  of  clay. 

Silt  loam  contains  more  than  55  per  cent,  of  silt  and  less  than  25 
per  cent,  of  clay. 

Loam  contains  less  than  55  per  cent,  of  silt,  and  more  than  50 
percent,  of  silt  and  clay,  usually  containing  from  15  to  25  per  cent, 
of  clay. 

Clay  loam  contains  from  25  to  55  per  cent,  of  silt,  25  to  35  per 
cent,  of  clay,  and  more  than  60  per  cent,  of  silt  and  clay. 

Clay  contains  more  than  35  per  cent,  of  clay. 

Sandy  clay  contains  more  than  30  per  cent,  of  coarse,  medium, 
and  fine  sand,  less  than  25  per  cent,  of  silt,  more  than  20  per 
cent,  of  clay,  and  less  than  60  per  cent,  of  silt  and  clay. 

Silt  clay  contains  more  than  55  per  cent,  of  silt  and  from  25  to 
35  per  cent,  of  clay. 

^^ 

OF  THE 

UNIVERSITY 

OF 


OF  THE 

UNlVERStT 


REVIEW  QUESTIONS 


CHAPTER  I. 

i.  From  what  are  soils  derived?  2.  What  are  the  physical  prop- 
erties of  soils  ?  3.  Why  do  soils  differ  in  weight?  Arrange  clay, 
sand,  loam,  and  peat  in  order  of  weight  per  cubic  foot.  4.  When 
wet,  what  would  be  the  order?  5.  What  is  the  absolute  and  what  the 
apparent  specific  gravity  of  soils?  6.  Define  the  terms  :  Skeleton,  fine 
earth,  fine  sand,  silt  and  clay.  7.  What  are  the  physical  properties 
of  clay  ?  8.  What  are  the  forms  of  the  soil  particles  ?  9.  How  do 
different  types  of  soil  vary  as  to  the  number  of  soil  particles  per 
gram  of  soil?  10.  How  is  a  mechanical  analysis  of  a  soil  made? 
ir.  Why  do  certain  crops  thrive  best  on  definite  types  of  soil  ?  12. 
What  factors  must  be  taken  into  consideration  in  determining  the 
type  to  which  a  soil  belongs?  13.  Explain  the  mechanical  struc- 
ture of  a  good  potato  soil.  14.  How  does  a  wheat  soil  differ  in 
mechanical  structure  from  a  truck  soil?  15.  A  good  corn  soil  is 
also  a  good  type  for  what  other  crops?  16.  How  much  water  is 
required  to  produce  an  average  grain  crop,  and  how  do  the  rainfall 
and  the  water  removed  in  crops  dtfring  the  growing  season  com- 
pare? 17.  In  what  forms  may  water  be  present  in  soils?  18. 
What  is  bottom  water  and  when  may  it  be  utilized  by  crops  ?  19. 
What  is  capillary  water?  20.  Explain  the  capillary  movement  of 
water.  21.  Explain  how  the  capillary  and  non-capillary  spaces  in 
the  soil  may  be  influenced  by  cultivation.  22.  What  is  hydro- 
scopic  water  and  of  what  value  is  it  to  crops  ?  23.  What  is  perco- 
lation ?  24.  To  what  extent  may  losses  occur  by  percolation  ?  25. 
What  are  the  factors  which  influence  evaporation  ?  26.  What  is 
transpiration  ?  27.  In  what  three  ways  may  water  be  lost  from  the 
soil?  28.  Why  does  shallow  surface  cultivation  prevent  evapora- 
tion ?  29.  Why  is  it  necessary  to  cultivate  the  soil  after  a  rain  ? 

30.  Explain  the  movement  of  the  soil  water  after  a  light  shower. 

31.  What  influence  has  rolling  the  land  upon  the  moisture  content 
of  the  soil  ?     32.    What  is  subsoiling  and  how  does  it  influence 
the   moisture  content  of  soils?     33.   What   influence  does  early 
spring  plowing  exert  upon  the  soil  moisture  ?     34.   What  is  the 
action  of  a  mulch  upon  the  soil?     35.  Why  should  different  soils 
be  plowed  to  different  depths?     36.   What  is  meant  by  the  per- 
meability of  a  soil?     37.   How  may  cultivation  influence  permea- 
bility of  a  soil  ?     38.   How  may  commercial  fertilizers  influence  the 
water  content  of  soils  ?     39.   Explain  the  physical  action  of  well- 
prepared  farm  manures  upon  the  soil  and  their  influence  upon  the 
soil  water.     40.  What  is  the  object  of  good  drainage?     41.   Why 
does  deforesting  a  region  unfavorably  influence  the  agricultural 
value  of  a  country  ?     42.  What  are  the  sources  of  heat  in  soils?  43. 


276  SOILS   AND   FERTILIZERS 

To  what  extent  does  the  color  of  soils  influence  the  temperature  ? 
44.  What  is  the  specific  heat  of  soils  ?  45.  To  what  extent  does 
drainage  influence  soil  temperature?  46.  How  do  manured  and 
unmanured  land  compare  as  to  temperature  ?  47.  VVhat  relation 
does  heat  bear  to  crop  growth  ?  48.  What  materials  impart  color 
to  soils?  49.  What  is  the  effect  of  loss  of  organic  matter  upon  the 
color  of  soils?  50.  What  materials  impart  taste  to  soils?  Odor? 
51.  WThat  effect  does  a  weak  current  of  electricity  have  upon  crop 
growth  ?  52.  Do  all  soils  possess  the  same  power  to  absorb  gases  ? 
Why? 

CHAPTER  II. 

53.  What  is  agricultural  geology?  54.  What  agencies  have 
taken  part  in  soil  formation  ?  55.  How  does  the  action  of  heat  and 
cold  aid  in  soil  formation  ?  56.  Explain  the  action  of  water  in 
soil  formation.  57.  What  is  glacial  action,  and  how  has  it  been  an 
important  factor  in  soil  formation  ?  58.  Explain  the  action  of 
vegetation  upon  soils.  59.  How  has  the  action  of  micro-organisms 
aided  in  soil  formation  ?  60.  Explain  the  terms :  Sedentary, 
transported,  alluvial,  colluvial,  volcanic,  and  windformed  soils. 
61.  What  is  feldspar  and  what  kind  of  soil  does  it  produce?  62. 
Give  the  general  composition  of  the  following  rocks  and  minerals 
and  state  the  quality  of  soil  which  each  produces  :  Granite,  mica, 
hornblende,  zeolites,  kaolin,  apatite,  and  limestone. 


CHAPTER  III. 

63.  What  elements  are  liable  to  be  the  most  deficient  in  soils? 

64.  Name  the  acid-  and  base-forming  elements  present  in  soils. 

65.  What  are  the  elements  most  essential  for  crop  growth  ?      66. 
State  some  of  the  different  ways  in  which  the  elements  present  in 
soils  combine.       67.  Why  is  it  customary  to  speak  of  the  oxides  of 
the  elements  and  to  deal  with  them  rather  than  with  the  elements  ? 
68.  Do  the  elements  exist  in  the  soil  in  the  form  of  oxides  ?    69. 
What  are  double  silicates  ?     70.  In  what  forms  does  carbon  occur  in 
soils  ?     71.   Is  the  soil  carbon  the  source  of  the  plant  carbon  ?      72. 
What  can  you  say  regarding  the  occurrence  and  importance  of  the 
sulphur  compounds  ?     73.  WThat  influence  would   o.  10  per   cent, 
chlorine  have  upon  the  soil  ?      74.  In  what  forms  does  phosphorus 
occur  in  soils?     75.  What  is  the  principal  form  in  which  the  nitro- 
gen occurs  in  soils  ?   76.  What  can  be  said  regarding  the  hydrogen 
and  oxygen  of  the  soil  ?     77.    State  the  principal   forms   and  the 
value  as  plant  food  of  the  following  elements:    Aluminum,  potas- 
sium, calcium,  sodium,  and  iron.       78.    For  plant  food  purposes, 
what  three  divisions  are  made  of  the  soil  compounds  ?     79.    Why 
are  the  complex  silicates  of  no  value  as  plant  food?      80.  Give  the 
relative  amounts  of  plant  food  in  the  three  classes.       81.    How  is  a 
soil  analysis  made?    82.  What  can  be  said  regarding  the  economic 


REVIEW   QUESTIONS  277 

value  of  a  soil  analysis?  83.  What  are  some  of  the  important  facts 
to  observe  in  interpreting  results  of  soil  analysis  ?  84.  Under  what 
conditions  are  the  results  most  valuable?  85.  Do  the  terms  volatile 
matter  and  organic  matter  mean  the  same  ?  86.  How  may  organic 
acids  be  employed  in  soil  analysis?  87.  Why  are  dilute  organic 
acids  used  ?  88.  Is  the  plant  food  equally  distributed  in  both  sur- 
face and  subsoil  ?  89.  Do  different  grades  of  soil  particles,  from 
the  same  soil,  have  the  same  composition?  90.  What  are  "alkali 
soils  "  ?  91.  Why  is  the  alkali  sometimes  in  the  form  of  a  crust? 
92.  Are  all  soils  with  white  coating  strongly  alkaline?  93.  Give 
the  treatment  for  improving  an  alkali  soil.  94.  How  may  a  small 
"  alkali  spot  "  be  treated  ?  95.  What  are  the  sources  of  the  organic 
compounds  of  soils  ?  96.  How  may  the  organic  compounds  of  the 
soil  be  classified?  97.  Explain  the  term  humus.  98.  How  is  the 
humus  of  the  soil  obtained  ?  99.  What  is  humification  ?  What  is 
a  humate  ?  How  are  humates  produced  in  the  soil  ?  100.  Explain 
how  different  materials  produce  humates  of  different  value.  101. 
Arrange  in  order  of  agricultural  value  the  humates  produced  from 
the  following  materials  :  Oat  straw,  sawdust,  meat  scraps,  sugar, 
clover.  102.  Of  what  value  are  the  humates  as  plant  food  ?  103. 
How  much  plant  food  is  present  in  soils  in  humate  forms  ?  104. 
What  agencies  cause  a  decrease  of  the  humus  content  of  soils? 
105.  To  what  extent  does  humus  influence  the  physical  properties 
of  soils?  106.  What  is  humic  acid?  107.  What  soils  are  most 
liable  to  be  in  need  of  humus?  When  are  soils  not  in  need  of 
humus?  108.  In  what  ways  does  the  humus  of  long-cultivated 
soils  differ  from  that  of  new  soils  ?  109.  How  many  different 
methods  of  farming  influence  the  humus  content  of  soils? 


CHAPTER  IV. 

no.  What  may  be  said  regarding  the  importance  of  nitrogen  as 
plant  food?  in.  What  are  the  functions  of  nitrogen  in  plant  nu- 
trition ?  112.  How  may  the  foliage  indicate  a  lack  or  an  excess  of 
this  element?  113.  In  what  three  ways  did  Boussingault  conduct 
experiments  relating  to  the  assimilation  of  the  free  nitrogen  of  the 
air?  114.  What  were  his  results?  115.  What  conclusions  did 
Ville  reach  ?  116.  Give  the  results  of  Lawes  and  Gilbert's  experi- 
ments. 117.  How  did  field  results  compare  with  laboratory  exper- 
iments? 1 1 8.  In  what  ways  were  the  conditions  of  field  experi- 
ments different  from  those  conducted  in  the  laboratory?  119. 
Give  the  results  of  Hellriegel's  and  Wilfarth's  experiments.  120. 
What  is  noticeable  regarding  the  composition  of  clover  root 
nodules?  121.  Of  what  agricultural  value  are  the  results  of  Hell- 
riegel  ?  122.  What  is  the  source  of  the  soil's  nitrogen  ?  123.  How 
may  the  organic  nitrogen  compounds  of  the  soil  vary  as  to  com- 
plexity ?  124.  To  what  extent  may  the  nitrogen  in  soils  vary? 
125.  To  what  extent  is  nitrogen  removed  in  crops?  126.  To  what 
extent  are  nitrates,  nitrites,  and  ammonium  compounds  found  in 


278  SOILS   AND   FERTILIZERS 

soils?  127.  To  what  extent  is  nitrogen  returned  to  the  soil  in 
rain-water?  128.  How  may  the  ratio  of  nitrogen  to  carbon  vary 
in  soils?  Of  what  agricultural  value  is  this  ratio  ?  129.  Under 
what  conditions  do  soils  gain  in  nitrogen  content  ?  130.  What 
methods  of  cultivation  cause  the  most  rapid  decline  in  the  nitro- 
gen content  of  soils?  131.  What  is  nitrification?  132.  What  are 
the  conditions  necessary  for  nitrification  ?  and  what  are  the  food 
requirements  of  the  nitrifying  organism  ?  133.  Why  is  oxygen 
necessary  for  nitrification  ?  134.  How  does  temperature,  moisture, 
and  sunlight  influence  this  process?  135.  What  part  does  calcium 
carbonate. and  other  basic  compounds  take  in  nitrification?  136. 
How  is  nitrous  acid  produced?  137.  What  is  denitrification  ?  138. 
What  other  organisms  are  present  in  soils  besides  those  which  pro- 
duce nitrates,  nitrites,  and  ammonia?  139.  What  chemical 
products  do  these  various  organisms  produce  ?  140.  Why  are  soils 
sometimes  inoculated  with  organisms?  141.  Why  does  summer 
fallowing  of  rich  lands  cause  a  loss  of  humus  and  nitrogen?  142. 
What  influence  have  deep  and  shallow  plowing,  and  spring  and 
fall  plowing  upon  the  available  soil  nitrogen  ?  143.  Into  what 
three  classes  are  nitrogenous  fertilizers  divided?  144.  How  is  dried 
blood  obtained?  What  is  its  composition,  and  how  is  it  used? 
145.  What  is  tankage?  How  is  it  used,  and  how  does  it  differ  in 
composition  from  dried  blood?  146.  What  is  flesh  meal ?  147. 
What  is  fish  scrap  fertilizer,  and  what  is  its  comparative  value  ? 
148.  What  seed  residues  are  used  as  fertilizer?  What  is  their 
value  ?  149.  What  method  is  employed  to  detect  the  presence  of 
leather,  hair,  and  wool  waste  in  fertilizers  ?  Why  are  these  ma- 
terials objectionable  ?  150.  How  may  peat  and  muck  be  used  as 
fertilizers?.  151.  What  is  sodium  nitrate?  How  is  it  used,  and 
what  is  its  value  as  a  fertilizer  ?  152.  How  does  ammonium  sul- 
phate, as  a  fertilizer,  compare  in  value  with  nitrate  of  soda?  153. 
What  is  the  difference  between  the  nitrogen  content  and  the  am- 
monia content  of  fertilizers  ? 


CHAPTERS  V  AND  VI. 

154.  What  is  fixation ?  Give  an  illustration.  155.  To  what  is 
fixation  due?  156.  What  part  does  humus  take  in  fixation?  157. 
Why  do  soils  differ  in  fixative  power  ?  Why  are  nitrates  not  fixed  ? 
158.  Why  is  fixation  a  desirable  property  of  soils?  159.  Why  is  it 
necessary  to  study  the  subject  of  fixation  in  the  use  of  manures? 
160.  Why  are  farm  manure?  variable  in  composition  ?  161.  What 
is  the  distinction  between  the  terms  stable  manure  and  farm-yard 
manure?  162.  About  what  per  cent,  of  nitrogen,  phosphoric  acid, 
and  potash  is  present  in  ordinary  manure?  -  163.  Coarse  fodders 
cause  an  increase  of  what  element  in  the  manure  ?  164.  W7hat 
four  factors  influence  the  composition  and  value  of  manure?  165. 
What  influence  do  absorbents  have  upon  the  composition  of 
manures?  166.  What  advantages  result  from  the  use  of  peat  and 


REVIEW   QUESTIONS  279 

muck  as  absorbents?  167.  Compare  the  value  of  manure  produced 
from  clover  with  that  from  timothy  hay.  168.  How  may  the  value 
of  manure  be  determined  from  the  nature  of  the  food  consumed  ? 
169.  To  what  extent  is  the  fertility  of  the  food  returned  in 
the  manure?  170.  Is  much  nitrogen  added  to  the  body  during  the 
process  of  fattening?  171.  Explain  the  course  of  the  nitrogen  of 
the  food  during  digestion  and  the  forms  in  which  it  is  voided  in 
the  manure.  172.  Compare  the  solid  and  liquid  excrements  as  to 
constancy  of  composition  and  amounts  produced.  173.  What  is 
meant  by  the  manurial  value  of  food  ?  174.  Name  five  foods  with 
high  manurial  values  ;  also  five  with  low  manurial  values.  175. 
What  is  the  usual  commercial  value  of  manures  compared  with 
commercial  fertilizers?  176.  How  does  the  manure  from  young 
and  from  old  animals  compare  as  to  value?  177.  How  much 
manure  does  a  well-fed  cow  produce  per  day  ?  178.  What  are  the 
characteristics  of  cow  manure  ?  How  do  horse  manure  and  cow 
manure  differ  as  to  composition,  character  and  fermentability  ? 
179.  What  are  the  characteristics  of  sheep  manure?  180.  How 
does  hen  manure  differ  from  any  other  manure  ?  181.  Why  should 
the  solid  and  liquid  excrements  be  mixed  to  produce  balanced 
manure?  182.  What  volatile  nitrogen  compound  may  be  given  off 
from  manure  ?  183.  What  may  be  said  regarding  the  use  of  human 
excrements  as  manure?  184.  Is  there  any  danger  of  an  immediate 
scarcity  of  plant  food  to  necessitate  the  use  of  human  excrements 
as  manure?  185.  To  what  extent  may  losses  occur  when  manures 
are  exposed  in  loose  piles  and  allowed  to  leach  for  six  months? 
186.  What  two  classes  of  ferments  are  present  in  manure?  187. 
Explain  the  workings  of  the  two  classes  of  ferments  found  in 
manures.  188.  How  much  heat  may  be  produced  in^  manure  dur- 
ing fermentation  ?  189.  Is  water  injurious  to  manure?  190.  How 
should  manure  be  composted?  What  is  gained  ?  191.  How  does 
properly  composted  manure  compare  in  composition  with  fresh 
manure?  192.  Explain  the  action  of  calcium  sulphate  in  the  pre- 
servation of  manure.  193.  How  does  manure,  produced  in  open 
barnyards  compare  in  composition  with  that  produced  in  covered 
sheds  ?  194.  When  may  manure  be  taken  directly  to  the  field  and 
spread?  195.  How  may  coarse  manures  be  injurious  to  crops? 
196.  What  is  gained  by  manuring  pasture  land?  197.  Is  it  econom- 
ical to  make  a  number  of  small  manure  piles  in  a  field?  Why? 
198.  At  what  rate  per  acre  may  manure  be  used?  199.  To  what 
crops  is  it  not  advisable  to  add  stable  manure  ?  200.  How  do  a 
crop  and  a  manure  produced  from  that  crop  compare  in  manurial 
value?  201.  Why  do  manures  have  such  a  lasting  effect  upon 
soils?  202.  Why  does  manure  from  different  farms  have  such 
variable  values  and  composition  ?  203.  In  what  seven  ways  may 
stable  manures  be  beneficial  ? 


CHAPTER  VII. 

204.  What  may  be  said  regarding  the  importance  of  phosphorus 


280  SOILS   AND   FERTILIZERS 

as  plant  food?  What  function  does  it  take  in  plant  economy? 
205.  How  much  phosphoric  acid  is  removed  in  ordinary  farm 
crops  ?  206.  To  what  extent  is  phosphoric  acid  present  in  soils  ? 
207.  What  are  the  sources  of  the  soil's  phosphoric  acid?  208  What 
are  the  commercial  sources  of  phosphate  fertilizers  ?  209.  Give 
the  four  calcium  phosphates  and  their  relative  fertilizer  values. 
210.  Define  reverted  phosphoric  acid.  211.  Define  available  phos- 
phoric acid.  212.  In  what  forms  do  phosphate  deposits  occur? 
213.  State  the  general  composition  of  phosphate  rock.  214.  Ex- 
plain the  process  by  which  acid  phosphates  are  made.  Give  re- 
actions. 215.  How  is  the  commercial  value  of  phosphoric  acid  de- 
termined? 216.  What  is  basic  phosphate  slag  and  what  is  its  value 
as  a  fertilizer?  217.  What  is  guano?  218.  How  do  raw  bone 
and  steamed  bone  compare  as  to  field  value  ?  As  to  composition  ? 
219.  What  is  dissolved  bone?  220.  How  is  bone-black  obtained, 
and  what  is  its  value  as  a  fertilizer?  221.  How  are  phosphate  fer- 
tilizers applied  to  soils?  In  what  amounts?  222.  How  may  the 
phosphoric  acid  of  the  soil  be  kept  in  available  condition  ? 


CHAPTER  VIII. 

223.  What  is  the  function  in  plant  nutrition  of  potassium  ?  224. 
To  what  extent  is  potash  removed  in  farm  crops?  225.  To  what 
extent  is  potash  present  in  soils?  226.  What  are  the  sources  of 
the  soil's  potash?  227.  What  are  the  various  sources  of  the  potash 
used  for  fertilizers  ?  228.  What  are  the  Stassfurt  salts,  and  how 
are  they  supposed  to  have  been  formed  ?  229.  What  is  kainit  ? 
230.  How  much  potash  is  there  in  hard-wood  ashes?  231.  In 
what  ways  do  ashes  act  on  soils?  232.  How  do  unleached  ashes 
differ  from  leached  ashes?  233.  What  is  meant  by  the  alkalimetry 
of  an  ash  ?  234.  Of  what  value,  as  fertilizer,  are  hard-  and  soft- 
coal  ashes?  235.  What  is  the  fertilizer  value  of  the  ashes  from 
tobacco  stems?  236.  Cottonseed  hulls?  237.  Peat-bog  ashes? 
238.  Saw-mill  ashes ?  239.  Lime-kiln  ashes?  240.  How  is  the 
commercial  value  of  potash  determined?  241.  How  are  potash 
fertilizers  used?  242.  Why  is  it  sometimes  necessary  to  use  a  lime 
fertilizer  in  connection  with  a  potash  fertilizer? 


CHAPTER  IX. 

243.  What  can  be  said  regarding  the  importance  of  lime  as  a 
plant  food?  244.  To  what  extent  is  lime  removed  in  crops?  245. 
To  what  extent  do  soils  contain  lime  ?  246.  What  are  the  lime  fer- 
tilizers? 247.  Explain  the  physical  action  of  lime  fertilizers.  248. 
Explain  the  action  of  lime  on  heavy  clays.  249.  On  sandy  soils. 
250.  In  what  ways,  chemically,  do  lime  fertilizers  act?  251.  How 
may  lime  aid  in  liberating  potash?  252.  What  is  marl?  253.  How 


REVIEW   QUESTIONS  281 

are  lime  fertilizers  applied  ?  254.  What  is  the  result  when  land 
plaster  is  used  in  excess?  255.  Explain  the  action  of  salt  on  soils. 
256.  When  would  it  be  desirable  to  use  salt  as  a  fertilizer?  257.  Is 
soot  of  any  value  as  a  fertilizer?  Explain  its  action.  258.  Are  sea- 
weeds of  any  value  as  fertilizer? 


CHAPTER  X. 

259.  What  is  a  commercial  fertilizer?      An  amendment?       260. 
To  what  does  the  commercial  fertilizer  industry   owe  its  origin  ? 

261.  Why  are  commercial  fertilizers  so  variable  in  composition? 

262.  Explain  how  a  commercial  fertilizer  is  made.      263.  Why  are 
the  analysis  and  inspection  of  fertilizers  necessary  ?       264.    What 
are  the  usual  forms  of  nitrogen  in  commercial  fertilizers?     265.  Of 
phosphoric  acid  and  potash  ?     266.  How  is  the  value  of  a  commer- 
cial fertilizer  determined?     267.  What  is  gained  by  home  mixing 
of  fertilizers?     268.    What   can   be   said   about  the  importance  of 
tillage  when  fertilizers  are  used  ?      269.    How  are  commercial  fer- 
tilizers sometimes  injudiciously  used?       270.    How  may  field  tests 
be  conducted  to  determine  a  deficiency  in  available  nitrogen,  phos- 
phoric acid,  or  potash?     271.    To  determine  a  deficiency  of  two 
elements?     272.    How  are  the  prelinilbary  results  verified ?     273. 
Why  is  it  essential  that  field  tests  with  fertilizers  be  made?     274. 
Under  what  conditions  does  it  pay  to  use  commercial  fertilizers  ? 
275.    What  is  the  result  when  commercial  fertliizers  are  used  in 
excessive  amounts?     276.  Under  ordinary  conditions,  what  special 
help  do  the  following  crops  require  :    Wheat,  barley,  corn,  potatoes, 
mangels,  turnips,  clover  and  timothy?     277.    In  what  ways  do 
commercial  fertilizers  and  farm  manures  differ? 


CHAPTER  XI. 

278.  Does  the  amount  of  fertility  removed  by  crops  indicate  the 
nature  of  the  fertilizer  required  ?  In  what  ways  are  plant  ash 
analyses  valuable  ?  279.  Explain  the  action  of  plants  in  render- 
ing their  own  food  soluble.  280.  Why  do  crops  differ  as  to  their 
power  of  procuring  food?  281.  Why  is  wheat  less  liable  to  need 
potash  than  nitrogen  ?  282.  What  position  should  wheat  occupy 
in  a  rotation  ?  283.  In  what  ways  do  wheat  and  barley  differ  in 
feeding  habits  ?  284.  What  can  be  said  regarding  the  food  require- 
ments of  oats  ?  285.  Corn  removes  from  the  soil  twice  as  much 
nitrogen  as  a  wheat  crop,  yet  a  wheat  crop  usually  thrives  after  a 
corn  crop.  Why  ?  286.  What  help  is  corn  most  liable  to  need  in 
the  way  of  food?  287.  What  position  should  flax  occupy  in  a 
rotation  ?  On  what  soils  does  flax  thrive  best  ?  289.  What  is  the 
essential  point  to  observe  in  the  manuring  of  potatoes  ?  290.  What 
kind  of  manuring  do  sugar-beets  require?  291.  Why  should  the 


282  SOILS   AND   FERTILIZERS 

manuring  of  mangels  be  different  from  that  of  turnips?  292.  What 
may  be  said  regarding  the  food  requirements  of  buckwheat  and 
rape?  293.  What  kind  of  manuring  do  hops  and  cotton  require ? 
294.  What  kind  of  manuring  is  most  suitable  for  leguminous 
crops  ?  For  garden  crops,  for  orchards,  or  lawns  ? 


CHAPTER  XII. 

295.  What  is  the  object  of  rotating  crops?  296.  Should  the 
whole  farm  undergo  the  same  rotation  system?  297.  What  is 
meant  by  soil  exhaustion  ?  298.  What  are  the  nine  important 
principals  to  be  observed  in  a  rotation  ?  299.  Explain  why  it  is 
essential  that  deep  and  shallow  rooted  crops  should  alternate  ? 
300.  Why  is  it  necessary  that  the  humus  be  considered  in  a  rota- 
tion ?  30 r.  What  is  the  object  of  growing  crops  of  dissimilar  feed- 
ing habits  ?  302.  How  may  crop  residues  be  used  to  the  best 
advantage  ?  303.  In  what  ways  may  a  decline  of  soil  nitrogen  be 
prevented  by  a  good  rotation  of  crops  ?  304.  In  what  ways  do 
different  crops  and  their  cultivation  influence  the  mechanical  con- 
dition of  the  soil  ?  305.  How  may  the  best  use  be  made  of  the  soil 
water  ?  306.  How  may  a  rotation  make  an  even  distribution  of 
farm  labor  ?  307.  How  are^manures  used  to  the  best  advantage  in 
a  rotation  ?  308.  In  what  other  ways  are  rotations  advantageous  ? 

309.  What  may  be  said  regarding  long  and  short-course  rotations? 

310.  How  is  the  conservation  of  fertility  best  secured?     311.  Why 
does  the  use  made  of  crops  influence  fertility  ?     312.    What  are  the 
essential  points  to  be  observed  in  the  two  systems  of  farming  com- 
pared in  Section   323?     313.    Is  it  essential   that  all  elements  re- 
moved  in   crops   should   be   returned   to  the   soil   in  exactly  the 
amounts  contained  in  the  crops?     Why?    314.    How  does  manure 
influence  the  inert  matter  of  the  soil  ?     315.    What  general  systems 
of  farming  best  conserve  fertility?     316.    Under  what  conditions 
may  farms  be  gaining  in  reserve  fertility  ?     317.    Why  in  continued 
grain  culture  does  the  loss  of  nitrogen  from  a  soil  exceed  the 
amount  removed  in  the  crop? 


CHAPTER  XIII. 

318.  Why  do  soils  need  further  treatment  for  the  preparation  of 
the  seed  bed?  319.  Why  should  different  soils  receive  different 
methods  of  treatment  in  the  preparation  of  the  seed  bed  ?  320. 
How  would  you  determine  the  best  treatment  to  give  a  soil  for  the 
preparation  of  the  seed  bed  ?  321.  How  do  different  methods  of 
plowing  influence  the  condition  of  the  seed  bed  ?  322.  Why  does 
complete  inversion  of  sod  frequently  form  a  poor  seed  bed  ?  323. 
How  should  the  plowing  be  done  to  form  a  good  seed  bed?  324. 
Why  is  it  economy  to  pulverize  the  soil  as  much  as  possible  when 
it  is  plowed?  325.  What  effect  does  the  moisture  content  of  the 


REVIEW   QUESTIONS  283 

soil  at  the  time  of  plowing  have  upon  the  condition  of  the  seed 
bed  ?  326.  What  effect  does  an  excess  of  moisture  have  upon  the 
plowing  and  working  of  clay  soils?  327.  In  what  condition 
should  the  seed  bed  be  left  as  to  fineness  ?  328.  What  is  gained 
by  fining  and  moderately  firming  the  seed  bed  ?  329.  Why  is 
aeration  of  the  soil  necessary?  330.  Why  do  different  soils  re- 
quire different  amounts  of  aeration?  331.  Under  what  conditions 
can  the  seed  bed  be  prepared  without  plowing?  332.  On  what 
kinds  of  soil  is  such  a  practice  not  advisable?  333.  When  is  it 
advisable  to  mix  the  sub  soil  with  the  surface  soil?  334.  When 
is  it  not  advisable  to  mix  the  surface  soil  and  sub  soil?  335. 
How  can  the  plowing  and  the  cultivation  of  the  soil  best  be  carried 
on  to  destroy  weeds?  336.  In  what  way  does  cultivation  influ- 
ence bacterial  action  in  the  soil?  337.  What  classes  of  com- 
pounds in  the  soil  are  subject  to  bacterial  action?  338.  How  does 
the  action  of  bacteria  affect  the  supply  of  available  plant  food  ? 
339.  What  is  meant  by  the  inoculation  of  soils?  340.  In  what 
two  ways  can  this  be  accomplished?  341.  What  soils  are  most 
improved  by  inoculation  ?  342.  What  soils  are  least  in  need  of 
inoculation  ?  343.  What  other  treatment  must  often  be  combined 
with  inoculation?  344.  Why  do  different  crops  require  different 
cultivation  ?  345.  How  can  the  best  kind  of  cultivation  for  a  crop 
be  determined?  346.  How  can  soils  best  be  cultivated  to  prevent 
washing  and  gullying?  347.  What  treatment  should  such  soils 
receive  to  be  permanently  improved?  348.  What  relationship 
exists  between  bacterial  diseases  of  soils  and  crops?  349.  What 
treatment  should  soils  receive  to  prevent  bacterial  diseases?  350. 
How  can  the  spreading  of  bacterial  diseases  through  infected  seed 
be  prevented?  351.  Why  must  the  sanitary  condition  of  a 
soil  for  crop  production  be  considered?  352.  What  effects  do 
some  forms  of  fungi  have  upon  soils?  353.  In  what  way  does 
thick  or  thin  seeding  affect  plant  growth?  354.  What  effect  does 
abnormal  crowding  of  plants  have  upon  growth?  355.  How 
would  you  determine  the  most  advantageous  quantity  of  seed  for 
crop  production  ?  356.  How  would  you  determine  the  most  suit- 
able crop  for  production  upon  any  soil?  357.  What  should  be 
the  aim  in  the  selection  of  crops  for  soils?  358.  Why  should  the 
crop  selected  vary  with  different  types  of  soil  ?  359.  What  is  the 
inherent  fertility  of  soils?  360.  What  is  the  cumulative  fertility 
of  soils?  361.  How  can  the  total  fertility  of  soils  be  best  in- 
creased? 362.  Describe  soils  of  the  highest  fertility.  363.  Why 
must  the  amount  of  plant  food  as  well  as  the  physical  condition  of 
the  soil  be  considered  in  the  improvement  of  soils  ?  364.  What 
relation  does  the  fertility  of  the  soil  bear  to  any  agricultural 
system  ? 


REFERENCES 

1.  Venable  :  History  of  Chemistry. 

2.  Gilbert  :  Inaugural  Lecture,  University  of  Oxford. 

3.  Liebig  :  Chemistry  in  Its  Applications  to   Agriculture  and 
Physiology. 

4.  Gilbert:  The  Scientific  Principles  of  Agriculture  (Lecture). 

5.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  30. 

6.  Stockbridge  :  Rocks  and  Soils. 

7.  Association  of  Official  Agricultural  Chemists,  Report  1898. 

8.  Maryland  Agricultural  Experiment  Station,  Bulletin  No.  21. 

9.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  41. 

10.  Osborne  :  Journal  of  Analytical  Chemistry,  Vol.  II,  Part  3. 

11.  Wiley  :  Agricultural  Analysis,  Vol.  I. 

12.  Hellriegel :  Calculated  from  Beitrage  zu  den  Naturwissen- 
schaft  Grandlagen  des  Ackerbaus. 

13.  King  :  Wisconsin  Agricultural  Experiment  Station,  Report 
1889. 

14.  Unpublished  results  of  author. 

15.  King  :  Soils. 

1 6.  Roberts  :  Fertility  of  the  Land. 

17.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  41. 

18.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  53. 

19.  Whitney  :  Division  of  Soils,  U.  S.  Department  of  Agriculture, 
Bulletin  No.  6. 

20.  Merrill :  Rocks,  Rock-weathering  and  Soils. 

21.  Miintz  :  Comptes  Rendus  de  1' Academic  des  Sciences,   CX 
(1890). 

22.  Storer  :  Agriculture,  Vol.  I. 

23.  Dyer:  Journal  of  the  Chemical  Society,  March,  1894. 

24.  Goss  :  Association  of  Official  Agricultural  Chemists,  Report 
1896. 

25.  Peter :  Association  of  Official  Agricultural   Chemists,  Report 
1895. 

26.  Loughridge  :  American  Journal  of  Science,  Vol.  VII  (1874). 

27.  Hilgard  :  Year-book  U.  S.  Department  of  Agriculture,  1895. 

28.  Houston  :  Indiana  Agricultural  Experiment  Station,  Bulle- 
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REFERENCES  285 

29.  Mulder  :  From  Mayer  :  Lehrbuch  der  Agrikulturchemie,  2. 

30.  Journal  of  the  American  Chemical  Society,  Vol.  XIX,  No.  9. 

31.  Year-book  U.  S.  Department  Agriculture,  1895. 

32.  Loughridge  :  South  Carolina  Agricultural  Experiment  Sta- 
tion, Second  Annual  Report. 

33.  Association  of  Official  Agricultural  Chemists,  Report  1893. 

34.  Washington     Agricultural     Experiment     Station,    Bulletin 
No.  13. 

35.  Association  of  Official  Agricultural  Chemists,  Report  1894. 

36.  California  Agricultural  Experiment  Station,  Report  1890. 

37.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  29. 

38.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  47. 

39.  Lawes  and  Gilbert :  Experiments  on  Vegetation,  Vol.  I. 

40.  Boussingault :  Agronomic,  Tome  I. 

41.  Atwater  :  American  Chemical  Journal,  Vol.  VI,   No.  8  and 
Vol.  VIII,  No.  5. 

42.  Hellriegel :  Welche  Stickstoff  Quellen  stehen  der  Pflanze  zu 
Gebote  ? 

43.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  34. 

44.  Warington  :  U.  S.  Department  of  Agriculture,  Office  of  Ex- 
periment Stations,  Bulletin  No.  8.  , 

45.  Hilgard  :  Association  of  Official  Agricultural  Chemists,  Re- 
port 1895. 

46.  Marchal:  Journal  of  the  Chemical  Society  (abstract),  June, 
1894. 

47.  Kiinnemann  :    Die      Landwirthschaftlichen      Versuchs-Sta- 
tionen,  50  (1898). 

48.  Adametz  :  Abstract,  Biedermann's  Centralblatt  fur  Agrikul- 
turchemie, 1887. 

49.  Atwater:  American  Chemical  Journal,  Vol.  IX  (1887). 

50.  Stutzer:  Biedermann's   Centralblatt  fur  Agrikulturchemie, 
1883. 

51.  Jenkins:  Connecticut   State    Agricultural   Experiment  Sta- 
tion, Report  1893. 

52.  Wagner  :  Biedermann's   Centralblatt  fur  Agrikulturchemie, 
1897. 

53.  Journal  of  the  Royal  Agricultural  Society,  1850. 

54.  From  Sachsse  :  Lehrbuch  der  Agrikulturchemie. 

55.  Lawes  and  Gilbert :  Experiments  with  Animals. 


286  SOILS   AND   FERTILIZERS 

56.  Beal :  U.  S.   Department  of  Agriculture,   Farmers'  Bulletin 
No.  21. 

57.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  26. 

58.  Mainly  from  Armsby  :  Pennsylvania    Agricultural    Experi- 
ment Station,   Report  1890.     Figures  for  grains   calculated  from 
original  data. 

59.  Heiden  :  Dungelehre. 

60.  Liebig  :  Natural  Laws  of  Husbandry. 

61.  Cornell  University  Agricultural  Experiment  Station,  Bulle- 
tins Nos.  13,  27  and  56. 

62.  Kinnard  :  From  Manures  and  Manuring  by  Aikman. 

63.  Wyatt :  Phosphates  of  America. 

64.  Wiley  :  Agricultural  Analysis,  Vol.  III. 

65.  Goessmann  :  Massachusetts  Agricultural  Experiment  Station, 
Report  i8Q4. 

66.  Connecticut  (State)  Agricultural  Experiment  Station,  Bulle- 
tin No.  103. 

67.  Goessmann:  Massachusetts  Agricultural  Experiment  Station, 
Report  1896. 

68.  Wheeler  :  Rhode   Island  Agricultural  Experiment  Station, 
Reports  1892,  1893,  etc. 

69.  Boussingault :  From  Storer :  Agriculture. 

70.  Handbook  of  Experiment  Station  Work. 

71.  New  York  (State)  Agricultural  Experiment  Station,  Bulle- 
tin No.  1 08. 

72.  Voorhees  :  U.  S.  Department  of  Agriculture,  Farmers'  Bul- 
letin No.  44. 

73.  Liebig  :  Die  Chemie  in    ihrer   Anwendung  auf    Agrikultur 
und  Physiologic. 

74.  Warington  :  Chemistry  of  the  Farm. 

75.  Lawes  and  Gilbert :  Growth  of  Wheat. 

76.  Lawes  and  Gilbert  :  Growth  of  Barley. 

77.  Lugger  :  Minnesota  Agricultural  Experiment  Station,  Bulle- 
tin No.  13. 

78.  Lawes  and  Gilbert  :  Growth  of  Potatoes. 

79.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  56. 

80.  Shaw  :  U.  S.  Department  or  Agriculture,  Farmers'  Bulletin 
No.  ii. 

81.  White  :  U.  S.  Department  of  Agriculture,  Farmers'  Bulletin 
No.  48. 


REFERENCES  287 

82.  Lawes  and  Gilbert  :  Permanent  Meadows. 

83.  Thompson  :  Graduating  Essay,   Minnesota  School  of  Agri- 
culture. 

84.  Nefedor :  Abstract,  Experiment  Station  Record,  Vol.  X,  No.  4. 

85.  Minnesota  Agricultural  Experiment  Station,  Bulletin  No.  89. 

86.  Journal  Analytical  and  Applied  Chemistry,  Vol.  VII,  No.  6. 

87.  Moore  :  U.  S.  Department  of  Agriculture,  Bureau  of  Plant 
Industry,  Bulletin  No.  71. 

88.  Meyer  :  Outlines  of  Theoretical  Chemistry. 

89.  Voorhees  :  Fertilizers. 

90.  Cornell  University  Experiment  Station,  Bulletin  No.  103. 

91.  Fraps  :  Annual  Report  1904,  Association  Official  Agricultural 
Chemists. 

92.  Illinois  Experiment  Station,  Bulletin  No.  93. 

93.  Canadian  Experiment  Farms,  Report  1903. 

94.  D.  Land.  Vers.  Stat.,  1899,  52- 

95.  A.  D.  Hall :  The  Soil. 


INDEIX 


Absorbents 133 

Absorption  of  heat  by  soils . .  39 

of  gases  by  soils .  269 

Absorptive  power  of  soils . . .  43 

Acid  soils 85 

Acid    soluble   matter,    of 

soils. 65,  269 

Acids  in  plant  roots 218 

Aeration  of  soils 250 

Aerobic  ferments 147 

Agricultural   geology 45 

Agronomy 8 

Air  movement  through  soils -266 

Albite 52 

Alchemy i 

Alkaline  soils 83 

Aluminum  of  soils 63 

Amendments,  soils 196 

Amonium  compounds 109 

salts 129 

Anaerobic  ferments 148 

Analysis  of  soil,  how  made • .  72 

value  of 74,  78 

Apatite  rock 54 

Apparatus,  list  of 262 

Application  of  fertilizer 212 

cf  manures 151,  154 

Arrangement  of   soil    parti- 
cles     14 

Ashes 182 

action  of,  on  soils  ....  183 

testing  of 272 

Assimilation  of  nitrogen ....   97 

of  phosphates 165 

Atmospheric  nitrogen 99 


Atwater 102,  125 

Availability  of  plant  food. . .   77 

Avail  able  phosphates...  1 68,  175 

nitrogen 108,  126 


Bacterial  action  and  cultiva- 
tion  115,  252 

Barley,  fertilizers  for 213 

food  requirements  of.  .220 

Blood,  dried  . . . .' 121 

Bone,  dissolved 174 

fertilizers 173 

Boneash 1 73 

Bone-black 174 

Boussingault's  experiments. 

ioo,  101,  399 

Calcium  as  essential  element.  187 
carbonate  and   nitrifi- 
cation   116 

compounds  of  soils. . .  64 

phosphate 55 

Capillary  water,    determina- 
tion of 263 

Capillarity 24 

and  cultivation 29 

Carbon  of  soil 60 

sources    for    plant 

growth 60 

Chlorine  of  soil 61,  83 

Citric    acid,    use    of  in   soil 

analysis 70 

Classification  of  soils,  scheme 

for 273 


INDEX 


289 


Clay,  formation  of 54 

particles 12 

sedimentation  of 267 

Clover  as  manure 127 

nitrogen  returned  by. 

102,  112,  245 

root  nodules 104 

manuring  of 226 

Coaf  ashes 184 

Color  of  plants,    influenced 

by  nitrogen 98 

of  soils 41 

and  soil  temperature . .  265 
Combination  of  elements  in 

soils 58 

Commercial  fertilizers  ..196-214 

abuse  of 206 

and  tillage 206 

and  farm  manures. ...  214 

composition  of 197 

extent  of  use 196 

field  tests  with 208 

for  special  crops 213 

home  mixing  of 204 

inspection  of   200 

judicious  use  of 207 

mechanical    condition 

of 200 

misleading  statements. 203 

nitrogen  of 200 

phosphoric  acid  of 201 

plant  food  in 199 

potash  of 202 

preparation  of 197 

valuation  of 203 

variable  composition  •   197 

Composition  of  soils 80,  82 

Composting  manures 149 

Corn,  fertilizers  for 213 

food  requirements  of.  .221 
and  manure 155 


Cotton,  fertilizers  for 224 

Cottonseed  meal 125 

Cow  manure 141 

Crop  residue 232 

Cultivation  after  rains 32 

and  bacterial  action.. 252 

shallow   surface 30 

and  soil  moisture  ....  265 
Cumulative  fertility 259 

Davy,  work  of 3 

Deficiency  of  nitrogen 209 

of  phosphoric  acid . .  •  •  210 

of  potash 210 

of  two  elements 211 

Denitrification 117 

De  Saussure,  work  of 3,  99 

Diseases  of  soils 256 

Dissolved  bone 1 74 

Distribution  of  soils 50 

Drainage .  28,  40 

Dried  blood 121 

Early  truck  soils 17 

Electricity  of  soil 43 

Evaporation 27 

Excessive  use  of  fertilizers.. 21 2 

Experiments 261,  274 

Experimental  plots 208 

Fallow  fields 119 

Fall  plowing 34 

Farm  manures 131,  159 

and  commercial  fertil- 
izers  214 

Feldspar 52,  199 

Fermentation  of  manures.    .  147 
Fertility,  conservation  of       241 

importance  of p  • .  260 

removed  in  crops 216 


2  go 


INDEX 


Fertilizers,  amount  to  use- .  -212 
influence    upon    soil 

water 37 

on  barley 213 

on  wheat 213 

Field  tests  with  fertilizers . . .  208 

Fine  earth 1 1 

Fish  fertilizer 125 

Fixation 160 

of  ammonia 161 

due  to  zeolites 160 

nitrates  not  fixed 161 

and   available   plant 

food 162 

Flax,  food  requirements  of.  .222 

soils 19 

Flesh  meal 124 

Forest  fires 92 

Formation  of  soils 45,  50 

Form  of  soil  particles 14 

Fruit  soils 18 

Fruit  trees,  fertilizers  for. .  -228 

Gains  of  humus 95 

of  nitrogen in 

Garden  crops,  fertilizers  for- 226 
Geological   study    of  soil, 

value  of 56 

Glaciers,  action  of 47 

Grain  soils 19 

Granite 54 

Grass  lands,  fertilizers  for- .  .225 

Grass  soils 19 

Guano 172 

Gullying  of  soils 255 

Gypsum  and  manure 149 

Hay  land,  fertilizing 225 

Heat  and  crop  growth 41 

produced  by  manures.  148 
of  soil 39-40 


Heiden 145,  150 

Hellriegel 22,  28,  105 

Hen  manure 143 

Hog  manure 143 

Hops,  fertilizers  for 225 

Hornblende 52 

Horse  manure 142 

Human  excrements 145 

Humates s   87 

as  plant  food 90 

Humification 87 

Humic  acid 94 

Hutnic  phosphates 88,  176 

Humus 87 

active  and  inactive  •  •  •  95 

causes  fixation 161 

composition  of 90 

extraction     of,    from 

soils 270 

loss  of,  from  soils 92 

soils  in  need  of 94 

Hydroscopic  moisture 26 

determination  of 262 

Importance  of  field  trials 211 

Income  and  outgo  of  fertil- 
ity    242-245 

Infected   seed   and  soil   dis- 
eases   256 

Inherent  fertility 259 

Injury  of  coarse  manures. 38,  152 

Inoculation  of  soils 119,  253 

Insoluble  matters  of  soils-67-68 
Iron  compounds  of  soil 65 

Kainit 180,  204 

Kaolin 54 

King 31.  33,  34 

Laboratory  note  book 261 

practice 262-274 


INDEX 


291 


Lawes  and  Gilbert. .  .6,  102,  219 

Lawn  fertilizers 228 

Leached  ashes 183 

Leaching  of  manure 146 

Leather 126 

Leguminous  crops,  fertilizers 

for 226 

as  manure 1 27 

nitrogen  assimilations 

of 102-105 

Liebig 5,  6,  145,  216 

Liquid  manure 136 

Lime,  action  on  soils 189 

amount  of,'  in  soils  •  •  •  188 
amount  removed  in 

crops 188 

excessive  use  of 192 

fertilizers , 188 

indirect  action  of 190 

physical  action  of 189 

use  of 192 

and  acid  soil 189 

and  clover 190 

Loam  soils 22 

Loss  of  fertility  in  grain  farm- 
ing  243 

Loss  of  humus 292 

nitrogen in,  119 

Losses  from  manures 146-7 

Magnesium     compounds    of 

soils 64 

salts  as  fertilizers  •  •  • .  193 

Mangels,  fertilizers  for 214 

Manure  from  cow 141 

hen 143 

hog 143 

horse 142 

sheep 142 

Manures,  farm 131 

composition  of 132 


Manures,  composting  of 149 

crop  producing  value.  139 
direct  application  of.  •  151 

fermentation  of 147 

influence    of,   on    soil 

temperature 264 

on  moisture 264 

influenced  by  foods.- 134 

leaching  of 146 

liquid 136 

mixing  of 144 

and  soil  water 37,  93 

use  of 151,  154 

use  of  in  rotation 235 

value  of 158 

Manurial  value  of  foods....  138 

Manuring  of  crops. .  • 154 

pasture  land 152 

Marl 191 

Mechanical  analysis  of  soils.   15 
condition  of  fertilizers.  200 
Methods   of  farming,   influ- 
ence of,  upon  fertil- 
ity    95 

Mica 53 

Micro-organisms  and  soil  for- 
mation   45,  49, 

Mixing  manures 144 

Movement    of    water    after 

rains 32 

Mulching 35 

Nitrate  of  soda '128 

Nitric  nitrogen 128 

Nitrification 113 

conditions  necessary 
for 113 

and  plowing 120 

Nitrogen,  assimilation  ..99,  102 

of  clover  plant  •  •  •  102,  105 

as  plant  food 97 


292 


INDEX 


Nitrogen,  compounds  of  soil.  61 
compounds,  solubility 

of 271 

deficiency  of,  in  soil . .  209 
loss  of,  by  fallowing.. 1 19 

losses  of,  from  soil 1 1 1 

ratio  of,  to  carbon no 

removed  in  crops....  108 
in    commercial    fertil- 
izers   200 

amount  of,  in  soils...  107 

in  organic  forms 106 

as  nitrates 109 

availability  of 107 

forms  of 106 

origin  of 106 

Nitrogenous  manures 121 

Number  of  soil  particles 15 

Odor  of  soils 42 

Organic  acids,  action  of,  upon 

soils 70-1 

Organic  compounds  of  soil, 

classification  of 86 

source  of 86 

Organic  nitrogen 121,  126 

Organisms,  ammonia  produc- 
ing  117 

of  soil 117 

nitrifying 114 

products  of 118 

Osborne 16 

Orthoclose 52 

Oxidation  of  soil 40 

Peat 127,  133 

Percolation 26 

Permanent  meadows,  manur- 
ing of 226 

Permeability  of  soils 36 


Phosphate  fertilizers .164 

commercial  forms 167 

manufacture  of 170 

as  plant  food 164 

removed  by  crops 165 

reverted 168 

rock 169 

slag 171 

use  of 171 

Phosphoric  acid  of  commer- 

mercial  fertilizers  ..167 

available 164,  176 

acid  in  soils 166 

acid,  deficiency  of 210 

removal  in  crops 165 

testing  for 271 

value  of 171 

Phosphorus    compounds    of 

soils 61 

Physical  analysis  of  soils  . . .  267 

property  of  soils 9 

modified  by  farming. .  96 

Plant  food,  classes  of  . 65-6 

ash  and  fertilizers 216 

distribution  of 78 

in  soil  solution  • . .  .66,  163 

Plants,  crowding  of,  in  seed 

bed 257 

Plowing,  depth  of 35 

energy  required  for . .  248 

fall 34 

spring 34 

influence  of,  on  soil  --249 
influence   of   moisture 

on 247 

influences   nitrifica- 
tion   247 

Potash  fertilizers 177 

use  of 185 

of    commercial    fertil- 
izers   202 


INDEX 


293 


Potash  in  soils,  sources  of- . .  1 79 
and  lime,  joint  use  of  •  185 

muriate  of •  •  •  .  181 

sulphate 181 

removed  in  crops 177 

Potassium  compounds  of  soil.  64 

Potato,  fertilizers  for 223 

food  requirements  of.  223 
soils 17 

Preliminary  trials,  with  fer- 
tilizers  208 

Pulverizing  soils 249 

Questions 275 


Rainfall    and    crop   produc- 
tion     23 

Rape,  food  requirements  of  .224 
Reaction  of  soils,  determina- 
tion of 268 

References 284-7 

Relation    of   crop    and    soil 

type 258 

Reverted  phosphoric  acid  •  • .  168 

Review  questions 275-283 

Roberts 36,  146,  248 

Rock  disintegration 45,  55 

Rocks,  composition  of 51,  56 

properties  of 268 

Rolling  of  soils 33,  249 

Roots,  action  on  soil... 214,  233 
Root  crops,  fertilizers  for  . .  .224 

Rotation  of  crops 230-7 

principals  involved ...  231 

length  of 236 

problems 237 

and  farm  labor 234 

and  humus 232 

and  insects 236 

and  soil  nitrogen 233 


Rotation  and  soil  water  .  •    .  234 
and  weeds 236 

Salt  as  a  fertilizer 193 

Sand,  grades  of 1 1,  13 

Seaweeds  as  fertilizers 194 

Sedentary  soils 50 

Seed,  amount  of  per  acre  •  •    257 

Seed  bed,  preparation  of 247 

Seed  residues 125 

Sheep  manure 142 

Silicon  and  silicates 59-60 

Silt  particles 12 

Size  of  soil  particles 1 1 

Skeleton  of  soils I  r 

Small  manure  piles •  •  •  153 

Sodium  compounds  of  soils.   65 

Soil,  composition  of 80- 1 

conservation  of  fertil- 
ity   241 

exhaustion 230,  259 

management 258 

particles,  study  of.  •  • .  268 

solution  of 65,  163 

types 17 

Soils  and   agriculture,    rela- 
tion of 260 

crops  suitable  for 258 

Soot 193 

Specific  gravity  of  soil 1 1 

Spring  plowing 34 

Stassfurt  salts-    180 

Stockbridge  . . «    1 1 ,  23 

Stock  farming  and  fertility . .  243 

Storer 60,  123 

Strand's  plant  ash 194 

Street  sweepings 194 

Stutzer 126 

Sub-soiling 33 

Sugar  beets,  fertilizers  for-  •  -223 
beet  soils 19 


294 


INDEX 


Sugar  beets  and  farm  man- 
ures   155 

Sulphate  of  potash 181 

Sulphur  compounds  of  soil . .  60 

Superphosphates 169 

Surface  sub-soil,  mixing  of.. 251 

Tankage 123 

Taste  of  soils 42 

Temperature  of  soils 39 

Tests  with  fertilizers 208 

Thaer,  work  of 3 

Tobacco,  manuring  of 155 

Tobacco  stems 184 

Transported  soils 50 

Truck  farming  and   fertiliz- 
ers   226 

Turnips,  fertilizers  for.. 214,  224 

Ville ioi 

Volcanic  soils 51 

Volume  of  soils 10 

Voorhees 204,  226 

Washing  of  land 255 

Water,  action  of,  upon  rocks 

and  soils 46 

in  rock  decay 48 

bottom 23 

capillary 24 

capillary  conservation 
of 29-30-1 


Water   holding    capacity   of 

soils 263 

hydroscopic 26 

losses  by  evaporation .   27 
losses  by  transpiration  28 

of  soil 23,  28 

of  soil  influenced 

by  drainage ....  28 
forest  regions  29 
manures  ....  37 
mulching  ...  35 
plowing  ....  34 

rolling 33 

sub-soiling  . .  33 
required  by  crops  ....  22 
soluble  matter  of  soils.  163 

Warington -US,  115.  116 

Weeds,    cultivation     to    de- 
stroy  251 

fertility  in 194 

Weight  of  soils 9 

how  determined 265 

Wheat,  fertilizers  for 213 

food  requirements  of.  .219 

soils 20-1 

Whitney 15,  44 

Wilfarth   104 

Wind  as  agent  in  soil  forma- 
tion    51 

Wood  ashes 182 

Wool  waste 1 26,  1 94 

Zeolites 53,  160 


O'  THE 

UNIVERSITY 

OF 


CORRECTIONS 

Page  7,  line  2,  "of  Uebig's"  not  "at 

Page  22,  line  16,  "there  are"  not  "they  are." 

Page  75,  page  heading,  "Silt  Analysis"  read  "Soil  Analysis." 

Page  94,  lines  14  and  15,  "humus"  not  "humis." 

Page  105,  line  12,  "propagated"  not  "propogated." 

Page  107,  line  6,  "insoluble"  not  "insoluable." 

Page  160,  line  9,  "instead"  not  "instread." 

Page  172,  line  23,  "guano  is"  not  "guano  and  is." 

Page  172,  line  29,  "is  now  found"  not  "are  now  found." 

Page  181,  line  26,  "Peaty  lands"  not  "party  lands." 

Page  183,  page  heading,  "Wool  Ashes"  read  "Wood  Ashes." 

Page  191,  line  n,  "acid  soils"  not  "acid  sods." 

Page  138,  line  25,  "manurial"  not  "inanural.,1 

Page  72,  reference  27  read  "86." 

Page  88,  reference  29  read  "18." 

Page  97,  reference  16  read  "17." 

Page  181,  reference  93  read  "92." 

Page  192,  reference  21  read  "22." 

Page  192,  reference  5  read  "89." 


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(3)  Chromic  Acid  Compounds. 

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